Eirdu, Carrier of Dawn // Isilu, Carrier of Twilight + Sin, Unending Cataclysm + Phyrexian Altar

Eirdu, Carrier of Dawn // Isilu, Carrier of Twilight

Sin, Unending Cataclysm

Phyrexian Altar

How it works

1. Activate Phyrexian Altar by sacrificing the additional creature.
2. When the creature dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
3. Activate Phyrexian Altar by sacrificing Sin.
4. When Sin dies, it triggers twice.
5. Resolve the first trigger, returning Sin from your graveyard to the battlefield with a -1/-1 counter on it. As Sin enters, remove the -1/-1 counter from the creature sacrificed in step 1, causing Sin to enter with a +1/+1 counter on it instead.
6. Resolve the second Sin trigger, putting the counters it had on it when it was sacrificed onto a creature you control and failing to shuffle it into your library as it's no longer in your graveyard.
7. Repeat.