Progenitor Mimic + Time Walk + Timeless Witness

Progenitor Mimic

Time Walk

Timeless Witness

How it works

1. Cast Time Walk by paying its mana cost, taking an extra turn after this one.
2. At the beginning of your next upkeep, Progenitor Mimic triggers, creating a token copy of Timeless Witness.
3. When the token Timeless Witness enters the battlefield, it triggers itself, returning Time Walk from your graveyard to your hand.
4. Repeat.

This Vintage-legal loop relies on Progenitor Mimic copying Timeless Witness to build a self-sustaining engine of infinite turns. During each of your upkeeps, the non-token Progenitor Mimic triggers to spawn a fresh token copy of Timeless Witness, which in turn exploits its enters-the-battlefield ability to fish Time Walk right back out of your graveyard. Once you cast Time Walk to take your extra turn, you simply untap, let the Mimic churn out another Witness, and repeat the cycle indefinitely to lock your opponent out of the game completely.