Please, show when diamond skin expires. Right now i have no information when spell is active, then suddenly my unit starts to take damage.

The best would an animation, kind of shield surrounding the unit, or at least a word "-diamond" going up.

Then there is a problem with AI - i tend to send one unit right in the middle of enemy with the spell on it, and invariably the unit gets swarm by all other units, and of course, attack do no damage whatsoever. AI should ignore 'immune' troops.