Saffi Eriksdotter + Mistmoon Griffin + Phyrexian Altar

Saffi Eriksdotter

Mistmoon Griffin

Phyrexian Altar

How it works

1. Activate Saffi by sacrificing it, targeting Mistmoon Griffin.
2. Activate Phyrexian Altar by sacrificing Mistmoon Griffin, adding one mana of any color.
3. When Mistmoon Griffin dies, it and Saffi trigger.
4. Resolve the Saffi trigger, returning Mistmoon Griffin from your graveyard to the battlefield.
5. Resolve the Mistmoon Griffin trigger, failing to exile it as it is not in your graveyard and then returning Saffi from your graveyard to the battlefield.
6. Repeat.