This couldn't counter pandemonium because the reverse time, hits big enough to kill etc would already have happened and there wouldn't be creatures to be targeted by this, other than frozen and poisoned.
I imagine you would allow this to fully heal creatures though so it would still be effective against many things. For example it could combo quite well with liquid shadow, rage potion or Acceleration. I like it, the theme is nice and I think the costing is fair. I already want to build a charger acceleration deck, and an Angel liquid shadow deck. Fun, balanced concept I reckon IF it fully heals. A side effect of removing cloak could work too.
Would this Fully Heal is the main question? If it is only usable as a situational counter then it won't get much use, because every game you draw it and the opponent doesn't have plague, freeze etc, it is a waste of a card.