Retreat to Coralhelm + Scaled Herbalist + Rakdos Carnarium

Retreat to Coralhelm

Scaled Herbalist

Rakdos Carnarium

How it works

1. Activate Scaled Herbalist by tapping it, putting Rakdos Carnarium from your hand onto the battlefield.
2. When Rakdos Carnarium enters the battlefield, it and Retreat to Coralhelm trigger.
3. Resolve the Rakdos Carnarium trigger, returning itself from the battlefield to your hand.
4. Resolve the Retreat to Coralhelm trigger, untapping Scaled Herbalist.
5. Repeat.