Stalwart Successor + Umbral Collar Zealot + Glen Elendra Archmage

Stalwart Successor

Umbral Collar Zealot

Glen Elendra Archmage

How it works

1. Activate Umbral Collar Zealot by sacrificing Glen Elendra Archmage
2. When Glen Elendra Archmage dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
3. When Glen Elendra Archmage enters, Stalwart Successor triggers, putting a +1/+1 counter on Glen Elendra Archmage
4. Resolve the Umbral Collar Zealot ability.
5. Repeat.