When Yannik leaves the battlefield, all creatures exiled with it return to the battlefield.
When Yannik enters the battlefield, it triggers, exiling another creature you control with power four or greater and putting at least four +1/+1 counters on Crystalline Crawler.
Activate Crystalline Crawler's first ability three times by removing three +1/+1 counters from it, adding ({3} magic symbol) .
Repeat.
Results
Infinite +1/+1 counters on all creatures you control except Yannik.