This mod randomly imbues spawning Living Things in the World with Diablo-style random Enchantments, making them much harder and much more rewarding to kill.

They also drop the quadruple amount of xp and a random enchanted item.

List of mods and what they do, as of 1.1.9

1UP - Mob heals fully, once, upon getting low
Alchimist - throws Potions at you
Berserk - Mob deals double damage, but hurts itself on attacking
Blastoff - Tosses Players into the air
Bulwark - Mob has 50% damage resistance
Choke - Drown on land, hit Mob to breathe for a moment
Cloaking - Invisibility Potion effect on Mob
Darkness - Blindness Potion effect on Player
Ender - can teleport dodge attacks, reflecting damage on the Player
Exhaust - Exhaust Potion effect on Player
Fiery - sets Player on Fire
Ghastly - shoots Fireballs
Gravity - knocks back or pulls Players
Lifesteal - heals from attacking
Ninja - can teleport dodge attacks, reflecting damage on the Player
Poisonous - poisons Player
Quicksand - Slow Potion effect on Player
Regen - heals Health back
Rust - causes high amounts of wear on weapons and armour when fought
Sapper - Hunger Potion effect on Player
Sprint - high movement speed bursts
Sticky - can snatch Items the Player attacks them with
Storm - calls down Lightning
Vengeance - reflects a portion of all damage done
Weakness - Weakness Potion effect on Player
Webber - spawns Webs at the Players legs
Wither - Wither effect

Download on my site as usual, changelog is included in every download.

AtomicStryker's Infernal Mobs