Anti-Venom, Horrifying Healer + Agatha's Soul Cauldron + Conclave Mentor + Walking Ballista

Anti-Venom, Horrifying Healer

Agatha's Soul Cauldron

Conclave Mentor

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 Conclave Mentor.
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.