Vigilance (Attacking doesn't cause this creature to taps.)
As Diamond Knight enters the battlefield, choose a color.
Whenever you cast a spell of the chosen color, put a +1/+1 counter on Diamond Knight.
, : Choose a card name, then reveal the top card of your library. If that card has the chosen name, sacrifice Diviner's Lockbox and draw three cards. Activate this ability only any time you could cast a sorcery.