Tainted Observer + Animation Module + Crystalline Crawler + Doubling Season + Tekuthal, Inquiry Dominus

Tainted Observer

Animation Module

Crystalline Crawler

Doubling Season

Tekuthal, Inquiry Dominus

How it works

1. Put a +1/+1 counter on a creature you control.
2. Animation Module triggers, causing you to pay 1 to create a 1/1 Servo artifact creature token.
3. The Servo enters the battlefield, triggering Tainted Observer, causing you to pay 2 to put four +1/+1 counters on Crystalline Crawler.
4. Animation Module triggers four times.
5. Resolve the first three Animation Module triggers, choosing not to pay.
6. Activate Crystalline Crawler's first ability three times by removing three +1/+1 counters from it, adding 3.
7. Resolve the final Animation Module trigger, causing you to pay 1 to create a 1/1 Servo artifact creature token.
8. Repeat from step 3.

This intricate engine relies on Crystalline Crawler acting as your mana battery and counter reservoir, supplying the fuel to keep the loop turning. Whenever Animation Module prompts you to pay for a Servo token, Tainted Observer triggers off that new creature entering the battlefield, letting you pay mana to proliferate. With Doubling Season and Tekuthal, Inquiry Dominus amplifying those effects, a single proliferation event cascades into an overwhelming surplus of +1/+1 counters on Crystalline Crawler. You can then pull those counters right back off for mana to sustain the loop while generating boundless tokens and growth.