First, The victim (the creature who is possessed) attempts to wrest back control over themselves.

Then the possessor bids an injury they are willing to take to maintain control.

If the possessor bids no injury, then the possessor is immediately expelled from the possessed creature's body, and the creature regains control over their body.

If the possessor bids an injury, the creature may then choose to take no injury or match the bid.

If the possessed creature does not take an injury, the possessor maintains control and takes their bidded injury.

If the possessed creature chooses to match the bid, then both creatures take the bidded injury. The creature then may choose to either expel your incorporeal body, or hold it prisoner in their body until the end of their next turn, at which point the former possessor may attempt to wrest back control in another spiritual battle.