Place one of your demons on a Lost Soul. While that demon remains, that Lost Soul cannot be rescued by a Hero. Discard that demon if holder loses two battle challenges. If the Lost Soul is taken out of play, discard that demon.
Acts 8:7 - For unclean spirits, crying with loud voice, came out of many that were possessed with them: and many taken with palsies, and that were lame, were healed.