The possessor exits Detheun the Fallen's body when in the boss fight of Act III, assuming that this is what possessed him. It must be defeated in order to finish the Campaign.
- Mind Control: Applies the Mental Condition "Mind Control" on a target (Attack adjacent allies, -5 Quickness, -25% Damage, 6+ seconds duration)
- Psychic Assault. Moderate Health Damage. Can stun. Drains 10 power.
The Possessor is an annoying mob: he has lots of health points and will just spam the threatening Mind Control skill. Try to neutralize him as fast as possible (drain his power, slow him, debuff him, kill him) and/or counter Mind Control (purify, remove the condition, use mental resist, etc).