Mikaeus, the Unhallowed + Ashcloud Phoenix + Phyrexian Altar

Mikaeus, the Unhallowed

Ashcloud Phoenix

Phyrexian Altar

How it works

1. Activate Phyrexian Altar by sacrificing Ashcloud Phoenix, adding one mana of any color.
2. When Ashcloud Phoenix dies, it triggers, as well as its undying ability if it does not have a +1/+1 counter on it.
3. Resolve the first trigger, returning it from your graveyard to the battlefield face-down.
4. Resolve the second trigger, doing nothing.
5. Activate Phyrexian Altar by sacrificing Ashcloud Phoenix, adding one mana of any color.
6. When Ashcloud Phoenix dies, it triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
7. Repeat.