Tourach's Chant + Dryad Arbor + Mikaeus, the Unhallowed + Pandemonium

Tourach's Chant

Dryad Arbor

Mikaeus, the Unhallowed

Pandemonium

How it works

1. Play Dryad Arbor.
2. When Dryad Arbor enters, Tourach's Chant and Pandemonium 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 Pandemonium trigger.
6. Resolve the Tourach's Chant trigger, putting a -1/-1 counter on Dryad Arbor.
7. Resolve the Pandemonium trigger, dealing damage to Dryad Arbor.
8. Repeat from step 4.

This loop transforms the humble Dryad Arbor into an infinite source of entering-the-battlefield, leaving-the-battlefield, and death triggers by leveraging the unique intersection of its creature and land types. Mikaeus, the Unhallowed provides the crucial undying engine, granting the land-creature a +1/+1 counter upon revival, while Tourach's Chant cleverly converts land drops or its own upkeep triggers into a repeatable -1/-1 counter that instantly strips away that protection to let it die again. Meanwhile, Pandemonium harnesses this endless cycle by dealing damage with each iteration, ultimately letting you obliterate any target.