Emeria Shepherd + Felidar Guardian + Phyrexian Altar

Emeria Shepherd

Felidar Guardian

Phyrexian Altar

How it works

1. Cast Felidar Guardian by paying 3.
2. Felidar Guardian enters the battlefield, blinking Plains.
3. Emeria Shepherd triggers.
4. Holding priority, activate Phyrexian Altar by sacrificing Felidar Guardian, adding one mana of any color.
5. Resolve the Emeria Shepherd trigger, returning Felidar Guardian from your graveyard to the battlefield.
6. Repeat from step 2.