Progenitor Mimic + Skullwinder + Time Walk

Progenitor Mimic

Skullwinder

Time Walk

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 Skullwinder.
3. When the token Skullwinder enters the battlefield, it triggers itself, returning Time Walk from your graveyard to your hand.
4. Repeat.

This Vintage-legal loop hinges on looping a single copy spell to chain infinite turns together. By casting Time Walk and letting it resolve into your graveyard, you set the stage for your upkeep. During that upkeep, Progenitor Mimic triggers to spit out a token copy of Skullwinder. The newly minted Skullwinder's enters-the-battlefield ability then forces its controller to scoop Time Walk right back out of the graveyard and into their hand, ready to be cast again for the next extra turn.