Sedris, the Traitor King, Void Maw, Altar of Dementia, and Witch Engine

Prerequisites

• Sedris, the Traitor King on the battlefield
• Void Maw on the battlefield
• Altar of Dementia on the battlefield
• Witch Engine on the battlefield
• available

Steps

1. Activate Altar of Dementia by sacrificing Witch Engine, causing target player to mill cards equal to Witch Engine's power
2. Activate Witch Engine's unearth ability by paying , returning it from your graveyard to the battlefield, giving it haste and exiling it at end of turn or when it leaves the battlefield
3. Activate Witch Engine by tapping it
4. Holding priority, activate Altar of Dementia by sacrificing Witch Engine
5. Both Witch Engine's undying ability and Void Maw attempt to exile Witch Engine when it would be put into your graveyard
6. Choose to apply the Void Maw replacement effect, exiling Witch Engine
7. Resolve the Witch Engine ability from step 3, adding
8. Resolve the Altar of Dementia ability, causing target player to mill cards equal to Witch Engine's power
9. Activate Void Maw by putting Witch Engine from exile into your graveyard, giving Void Maw +2/+2 until end of turn
10. Repeat from step 2

Results

• Infinite black mana
• Infinite ETB
• Infinite LTB
• Infinitely large Void Maw until end of turn
• Infinite mill
• Infinite sacrifice triggers
• Infinite self-mill