Yenna, Redtooth Regent + Ashnod's Altar + Enchanted Evening + Corridor Monitor

Yenna, Redtooth Regent

Ashnod's Altar

Enchanted Evening

Corridor Monitor

How it works

1. Activate Yenna by paying 2 and tapping it, creating a token copy of Corridor Monitor.
2. When the Corridor Monitor token enters, it triggers, untapping Yenna.
3. Activate Ashnod's Altar by sacrificing the Corridor Monitor token, adding CC.
4. Repeat.

By introducing Enchanted Evening to the battlefield, every single permanent you control—including Yenna, Redtooth Regent herself—becomes an enchantment in addition to its other types. This global transformation lets Yenna target your Corridor Monitor, using her tap ability to spawn a non-legendary token copy of it. When that Corridor Monitor token enters the battlefield, its triggered ability untaps Yenna, while Ashnod's Altar eagerly converts the token into a pair of colorless mana to feed the next iteration. This creates a self-sustaining loop that produces infinite creature entry, departure, and sacrifice triggers.