Kotis, Sibsig Champion + Altar of Dementia + Returned Pastcaller

Kotis, Sibsig Champion

Altar of Dementia

Returned Pastcaller

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