Ice Bull is a boss mob added by the Better Dungeons mod. It can be found in Ice Caves and serves as the boss mob for that structure. The Ice Bull uses a single charging attack that is very fast. It is able to race across the ice and slam the player for several hearts worth of damage.
It will destroy any blocks nearby when charge-attacking, the only exception is bedrock, so it is not recommended to fight this mob near important structures.
It will replace any air block below it's feet into Ice blocks.
The 'Spawn Egg' for this mob is called Bull instead of Ice Bull.
Because of it's ability to replace air to Ice, it is possible to create Ice farm using Ice Bull, however, it is hard to impossible because the Ice Bull will target you while farming the ice.