Mikaeus, the Unhallowed + Altar of Dementia + Obstinate Gargoyle

Mikaeus, the Unhallowed

Altar of Dementia

Obstinate Gargoyle

How it works

1. Activate Altar of Dementia by sacrificing Obstinate Gargoyle.
2. When Obstinate Gargoyle dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
3. Resolve the Altar of Dementia ability.
4. Activate Altar of Dementia by sacrificing Obstinate Gargoyle.
5. When Obstinate Gargoyle dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
6. Resolve the Altar of Dementia ability.
7. Repeat.