Vial of Blood

The Vial of Blood summons a pet Bat when used. It grants the Pet Bat buff that lasts until the player manually cancels it by right-clicking the buff's icon, or dies. Unlike other pets the pet bat will deal little damage enemies it happens to touch. Also, when a player is in water, the bat will fly above the water like the other bats.

Obtaining
It can be found in Golden Chests.