Anti-Venom, Horrifying Healer + Agatha's Soul Cauldron + Triskelion + Pir, Imaginative Rascal

Anti-Venom, Horrifying Healer

Agatha's Soul Cauldron

Triskelion

Pir, Imaginative Rascal

How it works

1. Activate Anti-Venom using Triskelion'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 Pir.
2. Activate Anti-Venom using Triskelion's ability by removing a +1/+1 counter from it, dealing 1 damage to any target.
3. Repeat.

This brilliant loop hinges on granting Triskelion's damage-dealing ability to Anti-Venom, Horrifying Healer through the power of Agatha's Soul Cauldron. Because Pir, Imaginative Rascal acts as a permanent multiplier whenever counters are placed, Anti-Venom's damage-prevention replacement effect actually generates a net surplus of +1/+1 counters every time it targets itself. You can then siphon off those extra counters to deal infinite damage to any target while endlessly sustaining the loop.