No thrull has ever been burdened with a long life.

Blood Pet

"You are wrong," Volrath said. "I do not hate the living. They often prove quite useful to me." And then he laughed.

The List

Seventh Edition

Sacrifice Blood Pet: Add o
B to your mana pool.

Classic Sixth Edition

Tempest

Sacrifice Blood Pet: Add o
B to your mana pool. Play this ability as a mana source.

Because combat damage resolves immediately after it is assigned, you cannot sacrifice Blood Pet in between assigning and dealing combat damage. The last chance you have to sacrifice it before combat damage is dealt is during the Declare Blockers step.