Opal, Serene Shot

Gem Fusion (When this enters the battlefield,
exile two other Gems you control and put a +1/+1
counter on this for each color it shares with those Gems.
Otherwise, sacrifice this. When this leaves the
battlefield, return those Gems to the battlefield under
their owners' control.)
{x}{r}{w}, {t}: Tap up to X target creatures. At
the beginning of the next end step, Opal, Serene
Shot deals X damage divided between those
creatures.