The Crowbell
The Crowbell is a Unique field boss located in the Hunting Grounds of Act 1.
He is found behine two sets of double doors. He stands atop a pillar at the end of a passage. If you dont kill him quickly he will run away and bust down the first set of double doors. After another short period, which of course will include attacking you, he will break down the second set of double doors, and you have to chase him into the Hunting Grounds.
He has a chance to drop a Book of Specialisation