Cloudseedling

Cloud (This creature has flying and can only block creatures with flying.)
Whenever Cloudseedling enters the battlefield or becomes a creature, put a 0/0 green Tree token with reach and a +1/+1 counter on the battlefield. Then, either proliferate or populate.
Crew 4 (Tap any number of creatures you control with total power of 4 or more: This vehicle becomes an artifact creature until end of turn.)