Progenitor Mimic + Eternal Witness + Time Walk

Progenitor Mimic

Eternal Witness

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