Walking Ballista Infinite Damage with Aveline and Vraska

Step 1: Cast Walking Ballista with sufficient counters (at least two).

Step 2: Use Walking Ballista's ability to remove a counter and deal damage to itself.

Step 3: Walking Ballista dies, triggering Vraska, Swarm Eminence to create a 1/1 deathtouch Assassin token.

Step 4: Aveline de Grandpré ensures you have a token to sacrifice or recur, maintaining board presence.

Step 5: Use Dark Ritual to recast Walking Ballista from your graveyard if necessary, using any recursion method.

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