Vial of Blood

The Vial of Blood summons a pet Bat when used. It grants the player the Pet Bat buff that lasts until the player manually cancels the buff or dies. Unlike other pets, the pet bat will deal a small amount of damage to enemies it happens to touch. Also, when a player is in a body of water, the bat will fly above it like any other type of bat.

Obtaining
It can be found in Golden Chests.