Sengir, the Dark Baron + Agatha's Soul Cauldron + Walking Ballista

Sengir, the Dark Baron

Agatha's Soul Cauldron

Walking Ballista

How it works

1. Give Sengir deathtouch, if needed.
2. Activate Sengir using Walking Ballista's second ability by removing a +1/+1 counter from it, dealing 1 damage to any creature an opponent controls, and killing it due to Sengir's deathtouch.
3. When the creature dies, Sengir's first ability triggers, putting two +1/+1 counters on it.
4. Repeat from step 2 as desired.

This fascinating loop relies on Agatha's Soul Cauldron to bridge Walking Ballista and Sengir, the Dark Baron together into a lethal engine. By granting Sengir the activated ability of Walking Ballista through the Cauldron, you can spend a counter to ping an opponent's creature; if you first ensure Sengir has deathtouch, that single point of damage is enough to kill it. The creature's death immediately triggers Sengir, the Dark Baron's first ability to place two +1/+1 counters on it, more than replacing the counter you spent and letting you repeat the process to completely wipe your opponents' boards and lock down the game.