Yenna, Redtooth Regent + Agatha's Soul Cauldron + Ashnod's Altar + Breaching Hippocamp

Yenna, Redtooth Regent

Agatha's Soul Cauldron

Ashnod's Altar

Breaching Hippocamp

How it works

1. Activate Breaching Hippocamp using the Licid's ability by paying its activation cost, attaching Breaching Hippocamp to Yenna and causing Breaching Hippocamp to become an Aura.
2. Activate Yenna by paying 2 and tapping it, creating a token copy of Breaching Hippocamp.
3. When the Breaching Hippocamp token enters, it triggers, untapping Yenna.
4. Activate Ashnod's Altar by sacrificing the Breaching Hippocamp token, adding CC.
5. Repeat from step 2.

By exiling Breaching Hippocamp into Agatha's Soul Cauldron, we grant its flash and enter-the-battlefield untap ability to Yenna, Redtooth Regent, provided Yenna has a +1/+1 counter. With this setup, Yenna can tap to create a token copy of an Aura, and when that token enters, it untaps Yenna to keep the loop going. Ashnod's Altar acts as our fuel and outlet, letting us sacrifice the copied tokens for colorless mana to pay for Yenna's ability over and over again.