Kotis, Sibsig Champion + Altar of Dementia + Zealous Lorecaster

Kotis, Sibsig Champion

Altar of Dementia

Zealous Lorecaster

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 Zealous Lorecaster, causing you to mill cards equal to Zealous Lorecaster's power.
4. Cast Zealous Lorecaster 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 Zealous Lorecaster enters the battlefield, it triggers, returning the extra turn spell from your graveyard to your hand.
6. Repeat.