Tourach's Chant + Dryad Arbor + Mikaeus, the Unhallowed + Warstorm Surge

Tourach's Chant

Dryad Arbor

Mikaeus, the Unhallowed

Warstorm Surge

How it works

1. Play Dryad Arbor.
2. When Dryad Arbor enters, Tourach's Chant and Warstorm Surge trigger.
3. Resolve the Tourach's Chant trigger, putting a -1/-1 counter on Dryad Arbor.
4. Dryad Arbor dies as a state-based action due to having 0 toughness, triggering its undying ability, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
5. When Dryad Arbor enters, Tourach's Chant and Warstorm Surge trigger.
6. Resolve the Tourach's Chant trigger, putting a -1/-1 counter on Dryad Arbor.
7. Resolve the Warstorm Surge trigger, dealing damage to Dryad Arbor.
8. Repeat from step 4.

This clever loop hinges on Mikaeus, the Unhallowed granting undying to non-Human creatures like Dryad Arbor, which conveniently doubles as a land and a creature. Because Dryad Arbor enters the battlefield as a Forest, it satisfies the condition of Tourach's Chant, forcing you to place a -1/-1 counter on it that instantly cancels out the +1/+1 counter from undying when it loops back from the graveyard. Meanwhile, every iteration lets Warstorm Surge trigger off Dryad Arbor's repeated entrances, turning this tragic little land into an endless artillery shell.