Codie, Vociferous Codex + Umbral Mantle + Heartstone

Codie, Vociferous Codex

Umbral Mantle

Heartstone

How it works

1. Activate Codie by paying 3 and tapping it, adding .
2. Activate Codie by paying 2 and untapping it, giving it +2/+2 until end of turn.
3. Repeat.
4. Once you have an arbitrarily large number of Codie triggers, you may cast any instant or sorcery by paying its mana cost, reduced by the added in step 1.
5. Codie triggers for each time you activated its ability.
6. Resolve the first trigger, causing you to exile cards from the top of your library until you exile an instant or sorcery spell with lesser mana value, and allowing you to cast that spell without paying its mana cost.
7. Repeat step 6 for each remaining trigger.
8. You may also repeat this combo for each instant and sorcery card in your hand as mana permits, and on subsequent turns.

This mesmerizing loop transforms Codie, Vociferous Codex into an infinite mana-generating and cascading engine by using Umbral Mantle to repeatedly untap it. While Codie's own restriction prevents you from casting permanent spells, Heartstone steps in to reduce the activation cost of Umbral Mantle down to just `{2}`, making the untap loop self-sustaining and capable of producing an arbitrarily large creature along with an abundance of rainbow mana. As you cycle through this activation loop, Codie triggers its ability over and over, allowing you to cascade through your library and cast every single instant or sorcery with a lesser mana value completely for free.