Kotis, Sibsig Champion + Altar of Dementia + Vampire Charmseeker

Kotis, Sibsig Champion

Altar of Dementia

Vampire Charmseeker

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