Donna Noble + Boros Reckoner

Prerequisites

You have a way to deal damage to Boros Reckoner. Boros Reckoner has indestructible.

Steps

1. Deal damage to Boros Reckoner
2. Donna Noble and Boros Reckoner trigger.
3. Resolve the Donna Noble trigger, dealing that much damage to an opponent.
4. Resolve the Boros Reckoner trigger, dealing that much damage to itself.
5. Repeat from step 2.