Progenitor Mimic + Time Stretch + Mnemonic Wall

Progenitor Mimic

Time Stretch

Mnemonic Wall

How it works

1. Cast Time Stretch by paying 8, taking two extra turns after this one.
2. At the beginning of your next upkeep, Progenitor Mimic triggers, creating a token copy of Mnemonic Wall.
3. When the token Mnemonic Wall enters the battlefield, it triggers itself, returning Time Stretch from your graveyard to your hand.
4. Repeat.