Prime Witch-Maw

Whenever a player casts a spell, you may put a
+1/+1 counter on Prime Witch-Maw.
At the beginning of combat on your turn, if
Prime Witch-Maw's power is 10 or greater, put
your choice of a vigilance, trample, deathtouch,
menace, reach, lifelink, or shield counter on it.
Counters remain on Prime Witch-Maw as it
moves to any zone other than a player's hand
or library.