Kotis, Sibsig Champion + Altar of Dementia + Shipwreck Dowser

Kotis, Sibsig Champion

Altar of Dementia

Shipwreck Dowser

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