Kotis, Sibsig Champion + Altar of Dementia + Archaeomancer

Kotis, Sibsig Champion

Altar of Dementia

Archaeomancer

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