Sin, Unending Cataclysm + Intruder Alarm + Altar of Dementia + Arbor Adherent

Sin, Unending Cataclysm

Intruder Alarm

Altar of Dementia

Arbor Adherent

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 Arbor Adherent by tapping it, adding an amount of or equal to Sin's toughness.
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 Arbor Adherent.
8. Resolve the Altar of Dementia ability.
9. Repeat.

This loop turns the recursive casting of Sin, Unending Cataclysm into an infinite engine by feeding its massive +1/+1 counter growth right back into your mana production and sacrifice outlets. As Sin enters the battlefield, it devours existing counters to grow huge, which immediately triggers Intruder Alarm to untap your board and allows Arbor Adherent to tap for a massive burst of colored mana based on that toughness. You then use Altar of Dementia to sacrifice Sin, milling your opponents while sending Sin back to the command zone so you can recast it and repeat the whole cycle.