Numion said:
What kind of badguy would ever think of such? If the BBEG had a possibility of coming up with such scheme, why not just make a room where all the PCs die and forget about any riddles?
Its a test of character, pardon the choice of words, to test those going up against the BBEG. It weakens them, builds a certain animosity between the protagonists and antagonists.
A lich (for example in this case) would like to only meet those he summons or those worthy of his challenging gauntlet.
If I were at the end of a series of rooms I'd like to know that those that have gotten to me are indeed worthy foes. Remember, at the end of the puzzles, rooms and monsters that the PC's are using up resources and will reach you rather tired.
To quote from Once Upon a Time in Mexico:
"The bull is stabbed, prodded, beaten. The bull is wounded. The bull is tired, before the matador ever steps into the ring. Now, is that victory? Of course it is."
and then on he goes about creative sportsmanship and rigging the odds.
Truely gruesome dungeons like the one from this campaign are the rinse cycle for the BBEG. They have time to build these places and set up ancient folk lore about themselves so some band of upshot hero wannabes can bust in, crawl tooth and nail to the objective then find out the objective has left or is fully prepared to murderdeathkill them.
BBEG's also sometimes want the only way in to be difficult. Imagine you're a cultist of said BBEG, you've got a pendant, training in the solutions, and in withstanding interrogation (or a quick death pill). Now, you can get in, through and to your master because you know the way. But those pesky 'Cormyr' people (for example) have to slog it out. Theres many unmitigating factors to creating these things. But the most important thing is that its for escapism from our daily life. If your daily life is solving puzzles and going from room to room fighting extraplanar beasts then maybe you could get a hobby as a checkout chick.
and as for the room that kills everyone, its been done and will continue to be done, Its funny to see players flailing about against certain doom when they failed the search spot and related checks for the giant pit trap of doom with added tobasco.