[Not part of Kornel’s kompilation.] I think it depends on the whole framework of code. In my world, for instance, making critters invisible is a rather simple task because of how I’ve implemented Line of Sight. Making them dead is harder :) That said: I find that balancing everything is a delicate task. Randomizing quests, equipments, races etc. is also an interesting challenge. Regarding these, however, I think its possible to find some short cuts just by writing imaginative pieces of sentences/elements and combining them in unpredictably large structures (needn’t be so huge). For example: put n kinds of “wandlikes” in a list (wands, lamps, bottles (uncork to release effect) etc.), have n kinds of “range models” (cones, rays, single adjacent/far points, zones (eg. fireball), clouds which start to drift and finally dissolve…), and n kinds of effects (elemental damage, teleport etc.). Already you’ll have weird objects popping up: from the presumably predictable (“copper wand: ray of ice”), by means of the useful (“painted calabash: cloud of panic”) and all the way to the outright silly (“ugly conjurers hat: rain of polymorph”).

Ramiro

Cellular Automata dungeons. (Even whit all the theory is STILL harder than you can think)
Anti-filescumming. (In theory is impossible, but you can make things harder)
Running (on ASCII Roguelikes, and turn based ones specially)