Toph, Greatest Earthbender + Power Depot + Crystalline Crawler + Yahenni, Undying Partisan + Shang-Chi, Martial Mentor

Toph, Greatest Earthbender

Power Depot

Crystalline Crawler

Yahenni, Undying Partisan

Shang-Chi, Martial Mentor

How it works

1. Play Power Depot, which will enter with a +1/+1 counter on it due to its modular ability
2. Cast Toph either from your hand or from the command zone by paying 2 plus commander tax if applicable.
3. When Toph enters, it triggers, earthbending Power Depot and putting a number of +1/+1 counters on Power Depot equal to the mana spent to cast Toph, increased by Shang-Chi.
4. Activate Yahenni by sacrificing Power Depot.
5. When Power Depot dies, its modular ability and Toph trigger.
6. Resolve the modular trigger, putting the +1/+1 counters that were on Power Depot onto Crystalline Crawler, increased by Shang-Chi.
7. Resolve the Toph trigger, returning Power Depot from your graveyard to the battlefield tapped. Power Depot will enter with a +1/+1 counter on it due to its modular ability
8. Resolve the Yahenni ability.
9. Activate Yahenni by sacrificing Toph. Choose to return Toph from your graveyard to the command zone.
10. Activate Crystalline Crawler by removing a +1/+1 counter from it, adding R/G.
11. Repeat step 10 until you have enough mana to cast Toph.
12. Repeat from step 2.

This intricate loop relies on Shang-Chi, Martial Mentor to dramatically amplify every counter movement, turning Toph, Greatest Earthbender and Power Depot into a self-sustaining engine. When Toph enters and earthbends Power Depot, Shang-Chi doubles the resulting counters, which are then fed into Crystalline Crawler and Yahenni, Undying Partisan upon sacrifice. This allows Crystalline Crawler to generate all the colored mana you need while Yahenni keeps the cycle safe and recurring, ultimately resurrecting Power Depot and recasting Toph to repeat the explosive process indefinitely.