Void Beam

The knight reaches a hand out and a large beam of negative energy shoots from their hand in a 30ft line which when any creature is hit by this beam they take 3d8 necrotic damage and must make a WIS save equal to your DC save or become possessed, being controlled by the user by bending and leaching of their soul if they have one. If the creature doesn't have a soul then this ability cannot work on them. If the creature dies while possessed their soul is leached and turned into a seal for the knight.

The targeted creature(s) may make a save at the end of each of their turns to end the effect.