Let's not make Charmyna into the Dark Destroyer here. Charmyna's a very good player and an even better spellbook designer (better than I at both) but not the grand champion who can never be defeated.
I have said nothing about a Dark Destroyer here or some one being one. Yes he is a very good player and is able to sus out very powerful card combo's. What I have suggested is to take a known build of his and have some play testers run against in number. That is the only way MW team will be able to determine if it is over powered or not. I can sit here all day and howl how powerful a card it is and nothing is going to change. It will have to be those who do the play testing to make the determination. With that said, it is still my opinion that the card is over powered for the combination of the four points in the OP itself. Cost/non-Zone Exclusiveness/Spellbind/not Epic. Tune one of the parameters here and you will bring the card back into balance.
A Steelclaw Grizzly has a mana cost of 17, is a full cast, I cant change him out with another creature every turn, his book cost (non-nature) is 8. So he is balanced.
- Make him a Quick Cast, unbalanced
- Make him cost 10 mana, unbalanced
- Let me change him out with another critter, brake the game
- Drop his level to 2, unbalanced
Here is the opposite of the Wizard Tower, if you make just one change on the Steelclaw he is very unbalanced. Honestly you could make a couple of change to the Tower and not break it or nerf it much. If you read through other threads here on the forums, you will clearly see that I am a staunch anti-nerf kind of guy. I have quit other game cold turkey. So for me to say something like this, I must think something is really broken.