Monsters can see player resistances

If monsters see you resist something, generally elemental or magical
attack, or if they see you reflect an attack, they learn that and
will adjust their attack accordingly.

Originally from SporkHack, but this version comes via EvilHack with
some minor changes.

doc/fixes37.0

@@ -990,6 +990,7 @@ using 'f' while quiver is empty and 'autoquiver' is Off when wielding a
 	the quiver (inspired by xNetHack)
 3.6's tribute: add one new passage to Sourcery, three to Small Gods, one to
 	Lords and Ladies, two to Soul Music
+monsters can see and remember hero resistances
 
 
 Platform- and/or Interface-Specific New Features

include/extern.h

@@ -1491,6 +1491,8 @@ extern const char *stagger(const struct permonst *, const char *);
 extern const char *on_fire(struct permonst *, struct attack *);
 extern const struct permonst *raceptr(struct monst *);
 extern boolean olfaction(struct permonst *);
+unsigned long cvt_adtyp_to_mseenres(uchar);
+extern void monstseesu(unsigned long);
 
 /* ### monmove.c ### */
 

include/monst.h

@@ -68,6 +68,23 @@ enum m_ap_types {
 #define M_AP_TYPE(m) ((m)->m_ap_type & M_AP_TYPMASK)
 #define M_AP_FLAG(m) ((m)->m_ap_type & ~M_AP_TYPMASK)
 
+enum m_seen_resistance {
+    M_SEEN_NOTHING = 0x0000,
+    M_SEEN_MAGR    = 0x0001, /* Antimagic, AD_MAGM */
+    M_SEEN_FIRE    = 0x0002, /* Fire_resistance, AD_FIRE */
+    M_SEEN_COLD    = 0x0004, /* Cold_resistance, AD_COLD */
+    M_SEEN_SLEEP   = 0x0008, /* Sleep_resistance, AD_SLEE */
+    M_SEEN_DISINT  = 0x0010, /* Disint_resistance, AD_DISN */
+    M_SEEN_ELEC    = 0x0020, /* Shock_resistance, AD_ELEC */
+    M_SEEN_POISON  = 0x0040, /* AD_DRST */
+    M_SEEN_ACID    = 0x0080, /* Acid_resistance, AD_ACID */
+    M_SEEN_REFL    = 0x0100, /* reflection, no corresponding AD_foo */
+};
+
+#define m_seenres(mon, mask) ((mon)->seen_resistance & (mask))
+#define m_setseenres(mon, mask) ((mon)->seen_resistance |= (mask))
+#define monstseesu_ad(adtyp) monstseesu(cvt_adtyp_to_mseenres(adtyp))
+
 struct monst {
     struct monst *nmon;
     struct permonst *data;
@@ -90,6 +107,7 @@ struct monst {
 
     schar mtame;                /* level of tameness, implies peaceful */
     unsigned short mextrinsics; /* low 8 correspond to mresists */
+    unsigned long seen_resistance; /* M_SEEN_x; saw you resist an effect */
     int mspec_used;             /* monster's special ability attack timeout */
 
     Bitfield(female, 1);      /* is female */

include/patchlevel.h

@@ -17,7 +17,7 @@
  * Incrementing EDITLEVEL can be used to force invalidation of old bones
  * and save files.
  */
-#define EDITLEVEL 32
+#define EDITLEVEL 33
 
 /*
  * Development status possibilities.

src/explode.c

@@ -529,6 +529,10 @@ explode(
             g.context.botl = 1;
         }
 
+	/* You resisted the damage, lets not keep that to ourselves */
+	if (uhurt == 1)
+	    monstseesu_ad(adtyp);
+
         if (u.uhp <= 0 || (Upolyd && u.mh <= 0)) {
             if (Upolyd) {
                 rehumanize();

src/fountain.c

@@ -542,9 +542,10 @@ drinksink(void)
         break;
     case 2:
         You("take a sip of scalding hot %s.", hliquid("water"));
-        if (Fire_resistance)
+        if (Fire_resistance) {
             pline("It seems quite tasty.");
-        else
+            monstseesu(M_SEEN_FIRE);
+        } else
             losehp(rnd(6), "sipping boiling water", KILLED_BY);
         /* boiling water burns considered fire damage */
         break;

src/makemon.c

@@ -1237,6 +1237,7 @@ makemon(register struct permonst *ptr,
 
     place_monster(mtmp, x, y);
     mtmp->mcansee = mtmp->mcanmove = TRUE;
+    mtmp->seen_resistance = M_SEEN_NOTHING;
     mtmp->mpeaceful = (mmflags & MM_ANGRY) ? FALSE : peace_minded(ptr);
 
     switch (ptr->mlet) {

src/mcastu.c

@@ -292,6 +292,7 @@ castmu(register struct monst *mtmp,
         if (Fire_resistance) {
             shieldeff(u.ux, u.uy);
             pline("But you resist the effects.");
+            monstseesu(M_SEEN_FIRE);
             dmg = 0;
         }
         burn_away_slime();
@@ -301,6 +302,7 @@ castmu(register struct monst *mtmp,
         if (Cold_resistance) {
             shieldeff(u.ux, u.uy);
             pline("But you resist the effects.");
+            monstseesu(M_SEEN_COLD);
             dmg = 0;
         }
         break;
@@ -309,6 +311,7 @@ castmu(register struct monst *mtmp,
         if (Antimagic) {
             shieldeff(u.ux, u.uy);
             pline_The("missiles bounce off!");
+            monstseesu(M_SEEN_MAGR);
             dmg = 0;
         } else
             dmg = d((int) mtmp->m_lev / 2 + 1, 6);
@@ -375,8 +378,10 @@ cast_wizard_spell(struct monst *mtmp, int dmg, int spellnum)
                 done(DIED);
             }
         } else {
-            if (Antimagic)
+            if (Antimagic) {
                 shieldeff(u.ux, u.uy);
+                monstseesu(M_SEEN_MAGR);
+            }
             pline("Lucky for you, it didn't work!");
         }
         dmg = 0;
@@ -425,6 +430,7 @@ cast_wizard_spell(struct monst *mtmp, int dmg, int spellnum)
     case MGC_DESTRY_ARMR:
         if (Antimagic) {
             shieldeff(u.ux, u.uy);
+            monstseesu(M_SEEN_MAGR);
             pline("A field of force surrounds you!");
         } else if (!destroy_arm(some_armor(&g.youmonst))) {
             Your("skin itches.");
@@ -434,6 +440,7 @@ cast_wizard_spell(struct monst *mtmp, int dmg, int spellnum)
     case MGC_WEAKEN_YOU: /* drain strength */
         if (Antimagic) {
             shieldeff(u.ux, u.uy);
+            monstseesu(M_SEEN_MAGR);
             You_feel("momentarily weakened.");
         } else {
             You("suddenly feel weaker!");
@@ -461,6 +468,7 @@ cast_wizard_spell(struct monst *mtmp, int dmg, int spellnum)
     case MGC_STUN_YOU:
         if (Antimagic || Free_action) {
             shieldeff(u.ux, u.uy);
+            monstseesu(M_SEEN_MAGR);
             if (!Stunned)
                 You_feel("momentarily disoriented.");
             make_stunned(1L, FALSE);
@@ -485,6 +493,7 @@ cast_wizard_spell(struct monst *mtmp, int dmg, int spellnum)
            made the spell virtually harmless to players with magic res. */
         if (Antimagic) {
             shieldeff(u.ux, u.uy);
+            monstseesu(M_SEEN_MAGR);
             dmg = (dmg + 1) / 2;
         }
         if (dmg <= 5)
@@ -528,6 +537,7 @@ cast_cleric_spell(struct monst *mtmp, int dmg, int spellnum)
         pline("A pillar of fire strikes all around you!");
         if (Fire_resistance) {
             shieldeff(u.ux, u.uy);
+            monstseesu(M_SEEN_FIRE);
             dmg = 0;
         } else
             dmg = d(8, 6);
@@ -549,8 +559,11 @@ cast_cleric_spell(struct monst *mtmp, int dmg, int spellnum)
         if (reflects || Shock_resistance) {
             shieldeff(u.ux, u.uy);
             dmg = 0;
-            if (reflects)
+            if (reflects) {
+                monstseesu(M_SEEN_REFL);
                 break;
+            }
+            monstseesu(M_SEEN_ELEC);
         } else
             dmg = d(8, 6);
         if (Half_spell_damage)
@@ -660,6 +673,7 @@ cast_cleric_spell(struct monst *mtmp, int dmg, int spellnum)
     case CLC_PARALYZE:
         if (Antimagic || Free_action) {
             shieldeff(u.ux, u.uy);
+            monstseesu(M_SEEN_MAGR);
             if (g.multi >= 0)
                 You("stiffen briefly.");
             nomul(-1);
@@ -679,6 +693,7 @@ cast_cleric_spell(struct monst *mtmp, int dmg, int spellnum)
     case CLC_CONFUSE_YOU:
         if (Antimagic) {
             shieldeff(u.ux, u.uy);
+            monstseesu(M_SEEN_MAGR);
             You_feel("momentarily dizzy.");
         } else {
             boolean oldprop = !!Confusion;
@@ -700,6 +715,7 @@ cast_cleric_spell(struct monst *mtmp, int dmg, int spellnum)
     case CLC_OPEN_WOUNDS:
         if (Antimagic) {
             shieldeff(u.ux, u.uy);
+            monstseesu(M_SEEN_MAGR);
             dmg = (dmg + 1) / 2;
         }
         if (dmg <= 5)

src/mhitu.c

@@ -1233,6 +1233,7 @@ gulpmu(struct monst *mtmp, struct attack *mattk)
     case AD_ACID:
         if (Acid_resistance) {
             You("are covered with a seemingly harmless goo.");
+            monstseesu(M_SEEN_ACID);
             tmp = 0;
         } else {
             if (Hallucination)
@@ -1264,6 +1265,7 @@ gulpmu(struct monst *mtmp, struct attack *mattk)
             if (Shock_resistance) {
                 shieldeff(u.ux, u.uy);
                 You("seem unhurt.");
+                monstseesu(M_SEEN_ELEC);
                 ugolemeffects(AD_ELEC, tmp);
                 tmp = 0;
             }
@@ -1275,6 +1277,7 @@ gulpmu(struct monst *mtmp, struct attack *mattk)
             if (Cold_resistance) {
                 shieldeff(u.ux, u.uy);
                 You_feel("mildly chilly.");
+                monstseesu(M_SEEN_COLD);
                 ugolemeffects(AD_COLD, tmp);
                 tmp = 0;
             } else
@@ -1287,6 +1290,7 @@ gulpmu(struct monst *mtmp, struct attack *mattk)
             if (Fire_resistance) {
                 shieldeff(u.ux, u.uy);
                 You_feel("mildly hot.");
+                monstseesu(M_SEEN_FIRE);
                 ugolemeffects(AD_FIRE, tmp);
                 tmp = 0;
             } else
@@ -1393,7 +1397,8 @@ explmu(struct monst *mtmp, struct attack *mattk, boolean ufound)
                 if (physical_damage)
                     tmp = Maybe_Half_Phys(tmp);
                 mdamageu(mtmp, tmp);
-            }
+            } else
+                monstseesu_ad(mattk->adtyp);
             break;
 
         case AD_BLND:
@@ -1596,6 +1601,7 @@ gazemu(struct monst *mtmp, struct attack *mattk)
                 stop_occupation();
                 if (Fire_resistance) {
                     pline_The("fire doesn't feel hot!");
+                    monstseesu(M_SEEN_FIRE);
                     dmg = 0;
                 }
                 burn_away_slime();

src/mondata.c

@@ -1223,4 +1223,36 @@ olfaction(struct permonst* mdat)
     return TRUE;
 }
 
+/* Convert attack damage type AD_foo to M_SEEN_bar */
+unsigned long
+cvt_adtyp_to_mseenres(uchar adtyp)
+{
+    switch (adtyp) {
+    case AD_MAGM: return M_SEEN_MAGR;
+    case AD_FIRE: return M_SEEN_FIRE;
+    case AD_COLD: return M_SEEN_COLD;
+    case AD_SLEE: return M_SEEN_SLEEP;
+    case AD_DISN: return M_SEEN_DISINT;
+    case AD_ELEC: return M_SEEN_ELEC;
+    case AD_DRST: return M_SEEN_POISON;
+    case AD_ACID: return M_SEEN_ACID;
+    /* M_SEEN_REFL has no corresponding AD_foo type */
+    default: return M_SEEN_NOTHING;
+    }
+}
+
+/* Monsters remember hero resisting effect M_SEEN_foo */
+void
+monstseesu(unsigned long seenres)
+{
+    struct monst *mtmp;
+
+    if (seenres == M_SEEN_NOTHING)
+        return;
+
+    for (mtmp = fmon; mtmp; mtmp = mtmp->nmon)
+        if (!DEADMONSTER(mtmp) && m_canseeu(mtmp))
+            m_setseenres(mtmp, seenres);
+}
+
 /*mondata.c*/

src/mthrowu.c

@@ -89,6 +89,7 @@ thitu(
 
         if (is_acid && Acid_resistance) {
             pline("It doesn't seem to hurt you.");
+            monstseesu(M_SEEN_ACID);
         } else if (obj && obj->oclass == POTION_CLASS) {
             /* an explosion which scatters objects might hit hero with one
                (potions deliberately thrown at hero are handled by m_throw) */
@@ -821,6 +822,14 @@ breamm(struct monst* mtmp, struct attack* mattk, struct monst* mtarg)
             }
             return MM_MISS;
         }
+
+	/* if we've seen the actual resistance, don't bother, or
+	 * if we're close by and they reflect, just jump the player */
+	if (m_seenres(mtmp, cvt_adtyp_to_mseenres(typ))
+	    || (m_seenres(mtmp, M_SEEN_REFL)
+                && monnear(mtmp, mtmp->mux, mtmp->muy)))
+	    return MM_HIT;
+
         if (!mtmp->mspec_used && rn2(3)) {
             if ((typ >= AD_MAGM) && (typ <= AD_ACID)) {
                 boolean utarget = (mtarg == &g.youmonst);

src/muse.c

@@ -1183,7 +1183,8 @@ boolean
 find_offensive(struct monst* mtmp)
 {
     register struct obj *obj;
-    boolean reflection_skip = (Reflecting && rn2(2));
+    boolean reflection_skip = m_seenres(mtmp, M_SEEN_REFL) != 0
+        || monnear(mtmp, mtmp->mux, mtmp->muy);
     struct obj *helmet = which_armor(mtmp, W_ARMH);
 
     g.m.offensive = (struct obj *) 0;
@@ -1208,42 +1209,50 @@ find_offensive(struct monst* mtmp)
     for (obj = mtmp->minvent; obj; obj = obj->nobj) {
         if (!reflection_skip) {
             nomore(MUSE_WAN_DEATH);
-            if (obj->otyp == WAN_DEATH && obj->spe > 0) {
+            if (obj->otyp == WAN_DEATH && obj->spe > 0
+                && !m_seenres(mtmp, M_SEEN_MAGR)) {
                 g.m.offensive = obj;
                 g.m.has_offense = MUSE_WAN_DEATH;
             }
             nomore(MUSE_WAN_SLEEP);
-            if (obj->otyp == WAN_SLEEP && obj->spe > 0 && g.multi >= 0) {
+            if (obj->otyp == WAN_SLEEP && obj->spe > 0 && g.multi >= 0
+                && !m_seenres(mtmp, M_SEEN_SLEEP)) {
                 g.m.offensive = obj;
                 g.m.has_offense = MUSE_WAN_SLEEP;
             }
             nomore(MUSE_WAN_FIRE);
-            if (obj->otyp == WAN_FIRE && obj->spe > 0) {
+            if (obj->otyp == WAN_FIRE && obj->spe > 0
+                && !m_seenres(mtmp, M_SEEN_FIRE)) {
                 g.m.offensive = obj;
                 g.m.has_offense = MUSE_WAN_FIRE;
             }
             nomore(MUSE_FIRE_HORN);
-            if (obj->otyp == FIRE_HORN && obj->spe > 0 && can_blow(mtmp)) {
+            if (obj->otyp == FIRE_HORN && obj->spe > 0 && can_blow(mtmp)
+                && !m_seenres(mtmp, M_SEEN_FIRE)) {
                 g.m.offensive = obj;
                 g.m.has_offense = MUSE_FIRE_HORN;
             }
             nomore(MUSE_WAN_COLD);
-            if (obj->otyp == WAN_COLD && obj->spe > 0) {
+            if (obj->otyp == WAN_COLD && obj->spe > 0
+                && !m_seenres(mtmp, M_SEEN_COLD)) {
                 g.m.offensive = obj;
                 g.m.has_offense = MUSE_WAN_COLD;
             }
             nomore(MUSE_FROST_HORN);
-            if (obj->otyp == FROST_HORN && obj->spe > 0 && can_blow(mtmp)) {
+            if (obj->otyp == FROST_HORN && obj->spe > 0 && can_blow(mtmp)
+                && !m_seenres(mtmp, M_SEEN_COLD)) {
                 g.m.offensive = obj;
                 g.m.has_offense = MUSE_FROST_HORN;
             }
             nomore(MUSE_WAN_LIGHTNING);
-            if (obj->otyp == WAN_LIGHTNING && obj->spe > 0) {
+            if (obj->otyp == WAN_LIGHTNING && obj->spe > 0
+                && !m_seenres(mtmp, M_SEEN_ELEC)) {
                 g.m.offensive = obj;
                 g.m.has_offense = MUSE_WAN_LIGHTNING;
             }
             nomore(MUSE_WAN_MAGIC_MISSILE);
-            if (obj->otyp == WAN_MAGIC_MISSILE && obj->spe > 0) {
+            if (obj->otyp == WAN_MAGIC_MISSILE && obj->spe > 0
+                && !m_seenres(mtmp, M_SEEN_MAGR)) {
                 g.m.offensive = obj;
                 g.m.has_offense = MUSE_WAN_MAGIC_MISSILE;
             }
@@ -1251,7 +1260,8 @@ find_offensive(struct monst* mtmp)
         nomore(MUSE_WAN_UNDEAD_TURNING);
         m_use_undead_turning(mtmp, obj);
         nomore(MUSE_WAN_STRIKING);
-        if (obj->otyp == WAN_STRIKING && obj->spe > 0) {
+        if (obj->otyp == WAN_STRIKING && obj->spe > 0
+            && !m_seenres(mtmp, M_SEEN_MAGR)) {
             g.m.offensive = obj;
             g.m.has_offense = MUSE_WAN_STRIKING;
         }
@@ -1285,12 +1295,14 @@ find_offensive(struct monst* mtmp)
             g.m.has_offense = MUSE_POT_CONFUSION;
         }
         nomore(MUSE_POT_SLEEPING);
-        if (obj->otyp == POT_SLEEPING) {
+        if (obj->otyp == POT_SLEEPING
+            && !m_seenres(mtmp, M_SEEN_SLEEP)) {
             g.m.offensive = obj;
             g.m.has_offense = MUSE_POT_SLEEPING;
         }
         nomore(MUSE_POT_ACID);
-        if (obj->otyp == POT_ACID) {
+        if (obj->otyp == POT_ACID
+            && !m_seenres(mtmp, M_SEEN_ACID)) {
             g.m.offensive = obj;
             g.m.has_offense = MUSE_POT_ACID;
         }
@@ -1315,7 +1327,8 @@ find_offensive(struct monst* mtmp)
         nomore(MUSE_SCR_FIRE);
         if (obj->otyp == SCR_FIRE && resists_fire(mtmp)
             && dist2(mtmp->mx, mtmp->my, mtmp->mux, mtmp->muy) <= 2
-            && mtmp->mcansee && haseyes(mtmp->data)) {
+            && mtmp->mcansee && haseyes(mtmp->data)
+            && !m_seenres(mtmp, M_SEEN_FIRE)) {
             g.m.offensive = obj;
             g.m.has_offense = MUSE_SCR_FIRE;
         }

src/potion.c

@@ -796,6 +796,7 @@ peffects(struct obj *otmp)
         break;
     case POT_SLEEPING:
         if (Sleep_resistance || Free_action) {
+            monstseesu(M_SEEN_SLEEP);
             You("yawn.");
         } else {
             You("suddenly fall asleep!");
@@ -1729,8 +1730,10 @@ potionbreathe(struct obj *obj)
             g.multi_reason = "sleeping off a magical draught";
             g.nomovemsg = You_can_move_again;
             exercise(A_DEX, FALSE);
-        } else
+        } else {
             You("yawn.");
+            monstseesu(M_SEEN_SLEEP);
+        }
         break;
     case POT_SPEED:
         if (!Fast)

src/pray.c

@@ -597,9 +597,11 @@ god_zaps_you(aligntyp resp_god)
                 pline("For some reason you're unaffected.");
             else
                 (void) ureflects("%s reflects from your %s.", "It");
+            monstseesu(M_SEEN_REFL);
         } else if (Shock_resistance) {
             shieldeff(u.ux, u.uy);
             pline("It seems not to affect you.");
+            monstseesu(M_SEEN_ELEC);
         } else
             fry_by_god(resp_god, FALSE);
     }
@@ -635,6 +637,7 @@ god_zaps_you(aligntyp resp_god)
         } else {
             You("bask in its %s glow for a minute...", NH_BLACK);
             godvoice(resp_god, "I believe it not!");
+            monstseesu(M_SEEN_DISINT);
         }
         if (Is_astralevel(&u.uz) || Is_sanctum(&u.uz)) {
             /* one more try for high altars */

src/read.c

@@ -1628,6 +1628,7 @@ seffects(struct obj *sobj) /* sobj - scroll or fake spellbook for spell */
             }
             else if (Fire_resistance) {
                 shieldeff(u.ux, u.uy);
+                monstseesu(M_SEEN_FIRE);
                 if (!Blind)
                     pline("Oh, look, what a pretty fire in your %s.",
                           makeplural(body_part(HAND)));

src/region.c

@@ -1002,6 +1002,7 @@ inside_gas_cloud(genericptr_t p1, genericptr_t p2)
             return FALSE;
         } else {
             You("cough!");
+            monstseesu(M_SEEN_POISON);
             return FALSE;
         }
     } else { /* A monster is inside the cloud */

src/trap.c

@@ -1251,6 +1251,7 @@ trapeffect_slp_gas_trap(
         seetrap(trap);
         if (Sleep_resistance || breathless(g.youmonst.data)) {
             You("are enveloped in a cloud of gas!");
+            monstseesu(M_SEEN_SLEEP);
         } else {
             pline("A cloud of gas puts you to sleep!");
             fall_asleep(-rnd(25), TRUE);
@@ -3525,6 +3526,7 @@ dofiretrap(
           the(box ? xname(box) : surface(u.ux, u.uy)));
     if (Fire_resistance) {
         shieldeff(u.ux, u.uy);
+        monstseesu(M_SEEN_FIRE);
         num = rn2(2);
     } else if (Upolyd) {
         num = d(2, 4);
@@ -5331,6 +5333,7 @@ chest_trap(
             if (Shock_resistance) {
                 shieldeff(u.ux, u.uy);
                 You("don't seem to be affected.");
+                monstseesu(M_SEEN_ELEC);
                 dmg = 0;
             } else
                 dmg = d(4, 4);
@@ -5763,6 +5766,8 @@ lava_effects(void)
         You("sink into the %s%s!", hliquid("lava"),
             !boil_away ? ", but it only burns slightly"
                        : " and are about to be immolated");
+        if (Fire_resistance)
+            monstseesu(M_SEEN_FIRE);
         if (u.uhp > 1)
             losehp(!boil_away ? 1 : (u.uhp / 2), lava_killer,
                    KILLED_BY); /* lava damage */

src/uhitm.c

@@ -2004,6 +2004,7 @@ mhitm_ad_fire(struct monst *magr, struct attack *mattk, struct monst *mdef,
                 return;
             } else if (Fire_resistance) {
                 pline_The("fire doesn't feel hot!");
+                monstseesu(M_SEEN_FIRE);
                 mhm->damage = 0;
             }
             if ((int) magr->m_lev > rn2(20))
@@ -2094,6 +2095,7 @@ mhitm_ad_cold(struct monst *magr, struct attack *mattk, struct monst *mdef,
             pline("You're covered in frost!");
             if (Cold_resistance) {
                 pline_The("frost doesn't seem cold!");
+                monstseesu(M_SEEN_COLD);
                 mhm->damage = 0;
             }
             if ((int) magr->m_lev > rn2(20))
@@ -2158,6 +2160,7 @@ mhitm_ad_elec(struct monst *magr, struct attack *mattk, struct monst *mdef,
             You("get zapped!");
             if (Shock_resistance) {
                 pline_The("zap doesn't shock you!");
+                monstseesu(M_SEEN_ELEC);
                 mhm->damage = 0;
             }
             if ((int) magr->m_lev > rn2(20))
@@ -2205,6 +2208,7 @@ mhitm_ad_acid(struct monst *magr, struct attack *mattk, struct monst *mdef,
             if (Acid_resistance) {
                 pline("You're covered in %s, but it seems harmless.",
                       hliquid("acid"));
+                monstseesu(M_SEEN_ACID);
                 mhm->damage = 0;
             } else {
                 pline("You're covered in %s!  It burns!", hliquid("acid"));
@@ -2881,8 +2885,10 @@ mhitm_ad_slee(struct monst *magr, struct attack *mattk, struct monst *mdef,
 
         hitmsg(magr, mattk);
         if (uncancelled && g.multi >= 0 && !rn2(5)) {
-            if (Sleep_resistance)
+            if (Sleep_resistance) {
+                monstseesu(M_SEEN_SLEEP);
                 return;
+            }
             fall_asleep(-rnd(10), TRUE);
             if (Blind)
                 You("are put to sleep!");
@@ -4881,6 +4887,8 @@ passive(struct monst *mon,
 
             if (!Acid_resistance)
                 mdamageu(mon, tmp);
+            else
+                monstseesu(M_SEEN_ACID);
             if (!rn2(30))
                 erode_armor(&g.youmonst, ERODE_CORRODE);
         }
@@ -4945,6 +4953,7 @@ passive(struct monst *mon,
         /* wrath of gods for attacking Oracle */
         if (Antimagic) {
             shieldeff(u.ux, u.uy);
+            monstseesu(M_SEEN_MAGR);
             pline("A hail of magic missiles narrowly misses you!");
         } else {
             You("are hit by magic missiles appearing from thin air!");
@@ -5021,6 +5030,7 @@ passive(struct monst *mon,
                 if (Cold_resistance) {
                     shieldeff(u.ux, u.uy);
                     You_feel("a mild chill.");
+                    monstseesu(M_SEEN_COLD);
                     ugolemeffects(AD_COLD, tmp);
                     break;
                 }
@@ -5044,6 +5054,7 @@ passive(struct monst *mon,
                 if (Fire_resistance) {
                     shieldeff(u.ux, u.uy);
                     You_feel("mildly warm.");
+                    monstseesu(M_SEEN_FIRE);
                     ugolemeffects(AD_FIRE, tmp);
                     break;
                 }
@@ -5055,6 +5066,7 @@ passive(struct monst *mon,
             if (Shock_resistance) {
                 shieldeff(u.ux, u.uy);
                 You_feel("a mild tingle.");
+                monstseesu(M_SEEN_ELEC);
                 ugolemeffects(AD_ELEC, tmp);
                 break;
             }

src/zap.c

@@ -2411,6 +2411,7 @@ zapyourself(struct obj *obj, boolean ordinary)
         if (Antimagic) {
             shieldeff(u.ux, u.uy);
             pline("Boing!");
+            monstseesu(M_SEEN_MAGR);
         } else {
             if (ordinary) {
                 You("bash yourself!");
@@ -2430,6 +2431,7 @@ zapyourself(struct obj *obj, boolean ordinary)
         } else {
             shieldeff(u.ux, u.uy);
             You("zap yourself, but seem unharmed.");
+            monstseesu(M_SEEN_ELEC);
             ugolemeffects(AD_ELEC, d(12, 6));
         }
         destroy_item(WAND_CLASS, AD_ELEC);
@@ -2447,6 +2449,7 @@ zapyourself(struct obj *obj, boolean ordinary)
         if (Fire_resistance) {
             shieldeff(u.ux, u.uy);
             You_feel("rather warm.");
+            monstseesu(M_SEEN_FIRE);
             ugolemeffects(AD_FIRE, d(12, 6));
         } else {
             pline("You've set yourself afire!");
@@ -2468,6 +2471,7 @@ zapyourself(struct obj *obj, boolean ordinary)
         if (Cold_resistance) {
             shieldeff(u.ux, u.uy);
             You_feel("a little chill.");
+            monstseesu(M_SEEN_COLD);
             ugolemeffects(AD_COLD, d(12, 6));
         } else {
             You("imitate a popsicle!");
@@ -2482,6 +2486,7 @@ zapyourself(struct obj *obj, boolean ordinary)
         if (Antimagic) {
             shieldeff(u.ux, u.uy);
             pline_The("missiles bounce!");
+            monstseesu(M_SEEN_MAGR);
         } else {
             damage = d(4, 6);
             pline("Idiot!  You've shot yourself!");
@@ -2551,6 +2556,7 @@ zapyourself(struct obj *obj, boolean ordinary)
         if (Sleep_resistance) {
             shieldeff(u.ux, u.uy);
             You("don't feel sleepy!");
+            monstseesu(M_SEEN_SLEEP);
         } else {
             pline_The("sleep ray hits you!");
             fall_asleep(-rnd(50), TRUE);
@@ -3875,6 +3881,7 @@ zhitu(int type, int nd, const char *fltxt, xchar sx, xchar sy)
         if (Antimagic) {
             shieldeff(sx, sy);
             pline_The("missiles bounce off!");
+            monstseesu(M_SEEN_MAGR);
         } else {
             dam = d(nd, 6);
             exercise(A_STR, FALSE);
@@ -3884,6 +3891,7 @@ zhitu(int type, int nd, const char *fltxt, xchar sx, xchar sy)
         if (Fire_resistance) {
             shieldeff(sx, sy);
             You("don't feel hot!");
+            monstseesu(M_SEEN_FIRE);
             ugolemeffects(AD_FIRE, d(nd, 6));
         } else {
             dam = d(nd, 6);
@@ -3905,6 +3913,7 @@ zhitu(int type, int nd, const char *fltxt, xchar sx, xchar sy)
         if (Cold_resistance) {
             shieldeff(sx, sy);
             You("don't feel cold.");
+            monstseesu(M_SEEN_COLD);
             ugolemeffects(AD_COLD, d(nd, 6));
         } else {
             dam = d(nd, 6);
@@ -3916,6 +3925,7 @@ zhitu(int type, int nd, const char *fltxt, xchar sx, xchar sy)
         if (Sleep_resistance) {
             shieldeff(u.ux, u.uy);
             You("don't feel sleepy.");
+            monstseesu(M_SEEN_SLEEP);
         } else {
             fall_asleep(-d(nd, 25), TRUE); /* sleep ray */
         }
@@ -3924,6 +3934,7 @@ zhitu(int type, int nd, const char *fltxt, xchar sx, xchar sy)
         if (abstyp == ZT_BREATH(ZT_DEATH)) {
             if (Disint_resistance) {
                 You("are not disintegrated.");
+                monstseesu(M_SEEN_DISINT);
                 break;
             } else if (uarms) {
                 /* destroy shield; other possessions are safe */
@@ -3948,6 +3959,7 @@ zhitu(int type, int nd, const char *fltxt, xchar sx, xchar sy)
             break;
         } else if (Antimagic) {
             shieldeff(sx, sy);
+            monstseesu(M_SEEN_MAGR);
             You("aren't affected.");
             break;
         }
@@ -3961,6 +3973,7 @@ zhitu(int type, int nd, const char *fltxt, xchar sx, xchar sy)
         if (Shock_resistance) {
             shieldeff(sx, sy);
             You("aren't affected.");
+            monstseesu(M_SEEN_ELEC);
             ugolemeffects(AD_ELEC, d(nd, 6));
         } else {
             dam = d(nd, 6);
@@ -3977,6 +3990,7 @@ zhitu(int type, int nd, const char *fltxt, xchar sx, xchar sy)
     case ZT_ACID:
         if (Acid_resistance) {
             pline_The("%s doesn't hurt.", hliquid("acid"));
+            monstseesu(M_SEEN_ACID);
             dam = 0;
         } else {
             pline_The("%s burns!", hliquid("acid"));
@@ -4309,6 +4323,7 @@ dobuzz(int type, int nd, xchar sx, xchar sy, int dx, int dy,
                                          "it");
                     } else
                         pline("For some reason you are not affected.");
+                    monstseesu(M_SEEN_REFL);
                     dx = -dx;
                     dy = -dy;
                     shieldeff(sx, sy);