This sets the minimum level depth of "Spider nest" to 10, somewhat above
the difficulty of an individual giant spider, because a whole room full
of them is a tougher challenge. Note that this isn't the only possible
fix to this problem; another solution would be to alter the special case
in mktrap that hardcodes a giant spider to generate with each web to
produce cave spiders if giant spiders would be too tough. Even then, a
lower difficulty cutoff is probably still warranted for this room, since
a large number of cave spiders might be too tough for level 1 or 2.
This also sets the minimum level depth of "Boulder room" to 4, based on
the fact that individual rolling boulder traps normally can't appear
until level 2, and having a bunch of them in one place which may be
required to reach the downstairs could be problematic.
This doesn't do anything to address the "Mausoleum" room problem, in
which a master or arch-lich can generate and immediately warp out and
attack the player. Even with a high difficulty threshold, it won't fix
the problem of these liches generating out of their normal difficulty
and Gehennom constraints.
Other potential candidates for difficulty thresholds:
- "Trap room": This room might be perilous on the first few levels,
especially if the level generates with it blocking the way to the
downstairs.
- "Massacre": Doesn't have any particular hazards, but might be
interesting if it only generated at deeper levels.