I thought up two concepts.
enemies have random drops, some monster-only drops, and some that all drop
you do random amounts of damage from a damage range that you can upgrade using skill points, same for enemies except they have a base range
I like the idea of random enemy drops. Skeletons could drop their skull and you could put a torch in it much like a jack o' lantern, Creepers could drop creeper skin or something like that, spiders could drop their legs (lol), zombies could drop feathers. Every mob could have some special thing that could only be dropped by the mob.
For those who have tested the arceolog(?) mod, it's a great example for a nice randomness factor.
For those who haven't, you can find fossils underground, when mined, a fossil could drop one of many items. (skull, some helmet, a sword, stone boards, dinosaur stuff etc.)