Da Big Talking Rock

During each player's end step, you may put
a +1/+1 counter on target creature. If you
do, that creature deals damage equal to its
power to a target creature, player or planeswalker chosen at random.
I fink it said "Beware of ambush." But I is Gnawbone of Rockland! 'Ow can I be Ware too? Stupid rock.