Cauldron of Souls + Corridor Monitor + Cathars' Crusade + Viscera Seer

Cauldron of Souls

Corridor Monitor

Cathars' Crusade

Viscera Seer

How it works

1. Activate Cauldron of Souls by tapping it, giving Corridor Monitor persist until end of turn.
2. Activate Viscera Seer by sacrificing Corridor Monitor.
3. When Corridor Monitor dies, its persist ability triggers, returning itself from your graveyard to the battlefield with a -1/-1 counter on it.
4. When Corridor Monitor enters the battlefield, it and Cathars' Crusade trigger.
5. Resolve the Corridor Monitor trigger, untapping Cauldron of Souls.
6. Resolve the Cathars' Crusade trigger, putting a +1/+1 counter on each creature you control.
7. Resolve the Viscera Seer ability from step 2, causing you to scry 1.
8. Repeat.