Gthbire, Adaptive War-Engine

Symbiosis (At the beginning of each opponent's upkeep, that player chooses a creature they control. Then, you may put a +1/+1 counter on that creature. If you do, put a +1/+1 counter on this creature.)
Creatures you control with power greater than their base power have trample and menace.
Creatures your opponents control with power greater than their base power can't block.