Progenitor Mimic + Time Stretch + Skullwinder

Progenitor Mimic

Time Stretch

Skullwinder

How it works

1. Cast Time Stretch 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 Stretch from your graveyard to your hand.
4. Repeat.