Trench Behemoth + Fastbond + Seraph Sanctuary

Steps

1. Activate Trench Behemoth by returning Seraph Sanctuary from the battlefield to your hand, untapping it.
2. Play Seraph Sanctuary, triggering its first ability and Fastbond.
3. Resolve the Seraph Sanctuary trigger, causing you to gain 1 life.
4. Resolve the Fastbond trigger, dealing 1 damage to you.
5. Activate Seraph Sanctuary by tapping it, adding {C}.
6. Repeat.