Genku, Future Shaper + Crystalline Crawler + Cryptic Trilobite + Solid Ground

Genku, Future Shaper

Crystalline Crawler

Cryptic Trilobite

Solid Ground

How it works

1. Activate Genku by paying 3, putting two +1/+1 counters on each creature you control due to Solid Ground
2. Activate Cryptic Trilobite's first ability twice by removing two +1/+1 counters from it, adding CCCC that can only be spent to activate abilities.
3. Activate Crystalline Crawler's first ability twice by removing two +1/+1 counters from it, adding .
4. Repeat.
5. Once you have infinite C, you may forego removing counters from Cryptic Trilobite.