Tainted Observer + Animation Module + Crystalline Crawler + Hardened Scales + Tekuthal, Inquiry Dominus

Tainted Observer

Animation Module

Crystalline Crawler

Hardened Scales

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 loop turns a simple spark of mana into a self-sustaining engine by cleverly chaining creature entries and counter manipulation. Crystalline Crawler acts as our primary battery and canvas, feeding on the surplus counters generated when Tainted Observer triggers off every new arrival and multiplies its output through Tekuthal, Inquiry Dominus's doubler effect. Meanwhile, Hardened Scales ensures that every single instance of counter placement yields an extra bonus, while Animation Module quietly converts those cascading +1/+1 counters into the exact stream of Servo tokens and mana needed to keep the entire cycle running indefinitely.