Darksteel Siege Engine

Indestructible, trample
Whenever Darksteel Siege Engine is crewed, it gets +1/+1 for each creature crewing it until end
of turn.
Multicrew 6 (Tap any number of creatures with total power 6 or more; then, tap any number of creatures with total power 6 or more: This Vehicle becomes an artifact creature until end of turn.)