Saffi Eriksdotter + Reveillark + Phyrexian Altar

Saffi Eriksdotter

Reveillark

Phyrexian Altar

How it works

1. Activate Saffi by sacrificing it, targeting Reveillark.
2. Activate Phyrexian Altar by sacrificing Reveillark, adding one mana of any color.
3. When Reveillark dies, it and Saffi trigger.
4. Resolve the Saffi trigger, returning Reveillark from your graveyard to the battlefield.
5. Resolve the Reveillark trigger, returning Saffi from your graveyard to the battlefield.
6. Repeat.