Sin, Unending Cataclysm + Intruder Alarm + Altar of Dementia + Selvala, Heart of the Wilds

Sin, Unending Cataclysm

Intruder Alarm

Altar of Dementia

Selvala, Heart of the Wilds

How it works

1. Cast Sin either from your hand or command zone by paying 5 plus commander tax if applicable.
2. As Sin enters, remove all counters from all artifacts, enchantments and creatures you control, putting twice that many +1/+1 counters on Sin.
3. When Sin enters, Intruder Alarm triggers, untapping all creatures.
4. Activate Selvala by paying and tapping it, adding at least plus an additional X equal to Sin's power minus 3.
5. Activate Altar of Dementia by sacrificing Sin.
6. Choose to return Sin to the command zone from your graveyard.
7. When Sin dies, it triggers, putting its counters on Selvala.
8. Resolve the Altar of Dementia ability.
9. Repeat.

This engine turns the cycle of casting and dying into an infinite storm of mana, untaps, and mill. Each time you cast Sin, Unending Cataclysm, its entry strips away existing counters from your board to amass a massive stack of +1/+1 counters on itself. That sudden arrival triggers Intruder Alarm to untap all creatures, letting you tap Selvala, Heart of the Wilds to harvest a massive influx of colored mana fueled by Sin's towering power. You then feed Sin to Altar of Dementia to mill your opponents out, letting the cataclysmic cat return to the command zone so you can loop the whole sequence anew.