Post by MandrakeI saw (here probably) that polymorph traps appear first on dungeon level
7, and also another source said that's where the first monsters that
freeze potions and burn scrolls appear. What does dungeon level 7
represent in the nethack mythology?
ISTR that polytraps start appearing with dlvl:8. There's nothing
special about that level only that some traps are considered too
dangerous (or unbalancing) and will not be created at shallow
levels (or in specific dungeon branches). Similar with monsters;
they have some difficulty metric associated and (roughly) can
only appear below certain levels (or in special levels). It's a
means to roughly balance the game difficulty depending on game
progress.
Of course there were traps that I still consider a problem (like
early magic traps) and that were not restricted . Also so called
out-of-depth-monsters were created (e.g. in polytraps or in form
of shape changing monster types).
Similar with countermeasures; a stoning cockatrice appears about
around the same level depths as lizard corpses, so you have a
change to prepare yourself. (But that doesn't mean it couldn't
happen that you don't meet a lizard before the cockatrice.)
And, yes, ISTR that e.g. winter wolves appear also around levels
5-9 (about around the Oracle level). But that's coincidence. All
monsters have some difficulty level (~ dungeon level range) where
they start appearing.
Disclaimer: I don't know whether anything has changed here since
version 343.
Janis