I was thinking of a card like this the other day, except I was going to call it something like Balance, wasn't sure if it should be gravity or entropy, and thought it could equalize HP as well as attack. That might be a little unfair given certain scnearios (using with Colossal Dragon or Armagio), so this seems pretty good. I still feel like there are some implications here for Butterfly Effect's potential uses.
Play a few RoL, build up a decent amount of light, Butterfly Effect one or two, then drop Light Dragons and balance. All of the sudden you've got something around a 6/1 RoL with destroy. Add blessings for more fun to protect your destroyers.
That's just one idea, I suppose it could work with other elements as well (Gravity using Armagio+Purple Dragon comes to mind for results that would be tougher to kill)