An ensouled bloodveld head is an item which can be dropped by bloodvelds. It is used to gain Prayer experience by using the level 65 Magic spell Reanimate Bloodveld from the Arceuus spellbook. Reanimating bloodvelds provides 1.5% Arceuus favour per head. Killing the reanimated bloodveld requires level 50 Slayer and will grant the player 1,040 Prayer experience.
The head can be reanimated anywhere across Gielinor only if the spell is cast on the head while it is still on the ground. Once the head has been picked up, it must be taken to the Dark Altar in Arceuus to be reanimated.
For an exhaustive list of all known sources for this item, see here