Anti-Venom, Horrifying Healer + Agatha's Soul Cauldron + Corpsejack Menace + Walking Ballista

Anti-Venom, Horrifying Healer

Agatha's Soul Cauldron

Corpsejack Menace

Walking Ballista

How it works

1. Activate Anti-Venom using Walking Ballista's ability by removing a +1/+1 counter from it, targeting itself and putting two +1/+1 counters on it due to its replacement effect and Corpsejack Menace.
2. Activate Anti-Venom using Walking Ballista's ability by removing a +1/+1 counter from it, dealing 1 damage to any target.
3. Repeat.

By exiling Walking Ballista with Agatha's Soul Cauldron, you grant its activated abilities to any creature you control that bears a +1/+1 counter. Anti-Venom, Horrifying Healer happily accepts this gift, especially since Corpsejack Menace doubles any +1/+1 counters that would be placed upon it. You can then repeatedly remove a counter to deal 1 damage, use the resulting prevention effect to feed Anti-Venom's damage-replacement ability, and net a surplus of counters to keep the loop going indefinitely.