The Master, Formed Anew | Ashnod's Altar

(and two other cards)

Persist Creature

Undying Creature

Persist Creature and Undying Creature in exile.
The Master and
Ashnod's Altar on the battlefield.
Both the persist and undying creatures are in exile with at least one takeover counter on them.
The Master on the battlefield as a copy of either the persist or undying creature.
The Master does not have a +1/+1 counter on it if it is a copy of the undying creature, or a -1/-1 counter on it otherwise.

Activate
Ashnod's Altar by sacrificing
The Master, adding ({C} magic symbol) ({C} magic symbol) .
When
The Master dies, if it was a copy of the undying creature, its undying ability triggers, returning it from your graveyard to the battlefield as a copy of the persist creature with a +1/+1 counter on it.
Otherwise, if
The Master was a copy of the persist creature, its persist ability triggers, returning it from your graveyard to the battlefield as a copy of the undying creature with a -1/-1 counter on it.
Repeat.