Walking Ballista Infinite Damage with Vraska and Aveline

Step 1: Have Vraska, Swarm's Eminence and Ashnod's Altar on the battlefield.

Step 2: Cast Walking Ballista with at least two +1/+1 counters.

Step 3: Use Walking Ballista's ability to remove a counter and deal 1 damage to a creature, triggering Vraska to create a deathtouch counter on Ballista.

Step 4: Use Aveline de Grandpré to create a creature token.

Step 5: Sacrifice the token to Ashnod's Altar for two colorless mana.

Step 6: Use the mana to add counters back to Walking Ballista and repeat the loop.

Step 7: Deal infinite damage to any target with Walking Ballista.