Denhead Moon: you did not get the helmet from the boss mob
GeoGaming: rare wither 0_0
Piotr Gruchalski: If you install Twilight Forest, it is a chance to spawn infernal Hydra. Infernal Ur-Ghast. With Mutant Creatures, you can met infernal mutant creeper. Or infernal mutant zombie. With Mo'Creatures, there are infernal werewolves and ogres. THIS is awesome!