Aveline and Walking Ballista Infinite Damage

Step 1: Have Aveline de Grandpré, Vraska, Swarm Eminence, Walking Ballista with at least one +1/+1 counter on it, and Ashnod's Altar on the battlefield.

Step 2: Remove a +1/+1 counter from Walking Ballista to deal 1 damage to a Deathtouch token created by Vraska.

Step 3: The Deathtouch token dies, triggering Aveline to place a +1/+1 counter on Walking Ballista.

Step 4: Sacrifice the Deathtouch token to Ashnod's Altar to generate 2 colorless mana.

Step 5: Use the mana to put a +1/+1 counter back on Walking Ballista.

Step 6: Repeat steps 2-5 to deal infinite damage to any target.