Kotis, Sibsig Champion + Altar of Dementia + Timeless Witness

Kotis, Sibsig Champion

Altar of Dementia

Timeless Witness

How it works

1. Cast the extra turn spell by paying its mana cost, causing you to take an extra turn after this one.
2. Move to your extra turn.
3. Activate Altar of Dementia by sacrificing Timeless Witness, causing you to mill cards equal to Timeless Witness's power.
4. Cast Timeless Witness from your graveyard by paying its mana cost and exiling three other cards from your graveyard, ensuring not to exile the extra turn spell.
5. When Timeless Witness enters the battlefield, it triggers, returning the extra turn spell from your graveyard to your hand.
6. Repeat.