Eirdu, Carrier of Dawn // Isilu, Carrier of Twilight + Mighty Mutanimals + Phantom Train
Infinite +1/+1 counters on a creature, Infinite ETB, Infinite LTB, Infinite death triggers, Infinite sacrifice triggers
Activate Phantom Train 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.
Resolve the Phantom Train ability.
Repeat.
Component Cards
How It Works
Activate Phantom Train 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.
Resolve the Phantom Train ability.
Repeat.