Tainted Observer + Animation Module + Crystalline Crawler + Branching Evolution + Tekuthal, Inquiry Dominus

Tainted Observer

Animation Module

Crystalline Crawler

Branching Evolution

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.