A Reanimated horror can be spawned with the spell Reanimate Horror. It can be reanimated where it was killed, but a player can only reanimate the ensouled head that they loot themselves. If a player teleports or trades the ensouled head, it must be reanimated by the Dark Altar. Killing the creature will grant the player 832 Prayer XP and +1.5% Favour to the Arceuus House (assuming you're not capped at 100%).
The player does not need to be wearing a Witchwood icon. They only count towards jungle horror Slayer tasks, not cave horrors.