How about: you have to push barrels of napalm into place. They cannot be destroyed, but if they get hit they spill lava all over the place. You have to push the barrels quickly into right place, otherwise you'll get flooded with lost souls (or other monsters on higher difficulty level) which spawn from time to time. Developer has to make sure, that monsters are spawned in a way, that will not prevent the hero from moving barrels into correct place. You don't get xp for the monsters!
This would be a good challenge for berserker. You can enter as a regular character but you'll have to watch not to damage the barrels during the carnage, otherwise you'll have to push barrels into lava.
Now what's next. Fight with another boss of doom? Or you can reward for completing the level?
Also, as this level is sort of a prank, it shouldn't appear very often. Only 1 out of 20 games? And it should be somewhere in Hell, so it also would make discovery of that level very rare.
I think that Lava Barrels are not very sokobanish. The Sokoban itself had a very narrow corridors, and lava/napalm would block the passages instantly.
The beauty of the game was to find a solution for a puzzle, not to wreak havoc around.
Second thing I do not like is creating a level for Berserker only. The times when it was the most challenging thing in DoomRL have passed. No need for more buffs.
The way I see it is a modification of yer idea:
- a part of a level (something around vault size) could be a Sokoban puzzle. The area itself could be surrounded by water to prevent taking other barrels there;
- Sokoban puzzle should be inaccessible for monsters (dead stuff on ground could make puzzle insolvable); an indestructible wall (and an associated lever) could be decent protection;
- once a puzzle is solved (all barrels are in positions), the other special part of level (presumably surrounded with unbreakable wall) would become accessible;
- that other part of level could have another part of Sokoban puzzle, or some boss to fight with, or some reward, or stairs to a special level, etc;
- the level itself should have flavour text about Sokoban puzzle existance; e.g. "Somehow you feel an urge to push things...", "Somehow you feel an urge to have everything in its place...";
Some examples of Sokoban puzzles:
http://www.youtube.com/watch?v=i_WmVBwEE4U (original game)
http://www.sourcecode.se/sokoban/levels.php