Eirdu, Carrier of Dawn // Isilu, Carrier of Twilight + Mighty Mutanimals + Phyrexian Altar
Infinite ETB, Infinite LTB, Infinite colored mana, Infinite death triggers, Infinite sacrifice triggers
Activate Phyrexian Altar by sacrificing another nontoken creature that doesn't have a -1/-1 counter on it.
When the creature dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
When the creature enters, Mighty Mutanimals triggers, putting a +1/+1 counter on the creature.
Repeat.
Component Cards
How It Works
Activate Phyrexian Altar by sacrificing another nontoken creature that doesn't have a -1/-1 counter on it.
When the creature dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
When the creature enters, Mighty Mutanimals triggers, putting a +1/+1 counter on the creature.
Repeat.