I actually forgot. This card synergizes extremely well with antimatter. You can even use this in a mono deck with entropy. *facepalm*
Antimattering would mean that you could ignore its ability completely. D'oh. Still, Combining this with antimatter, you'll be paying 10+6

for only 13 damage on a pretty CC proof creature. Not too good of a deal. Again, dragons would be more efficient at this rate. Now if it started with -16.... hmm... That could potentially work out. You'll be paying 16

or a nymph, and 14

for each reversed clockwork for 16 damage. That makes it quite balanced, as the damage to cost ratio is near one. I really don't see why it has the growing health and losing health when using its ability concept.
Just make it into something like, Reversed Clockwork 10

-16|5 ability

invert the attack of this creature for one turn.
TL;DR: Even combined with antimatter, this card is pretty weak. I suggest making it start with -16atk, and get rid of its health growing and health losing.