1) Still regarding the general power of Entropy Animus
a) "any rainbow can generate enough quanta to power the opponent's deck"
Try taking any mono deck and replacing its towers with quantum towers..That's how effective the cards you gain through Entropy Animus's effect will be
b) "when this goes off it's like a first turn with his deck"
Again, these cases are rare, since you need 6+ Entropy creatures in your deck and enough quanta to play the Entropy creatures you drew and the extra Entropy Animi.
c) "6 lycans [...] and many maxwells should suffice"
So you want quantum towers for rainbow quanta generation...and run all those entropy creatures off the mark?!
d) "7 card mill is a lot when a good portion of the decks are 30 cards"
While this may sound counter-intuitive, Entropy Animus is actually weaker against 30-card decks. The most viable 30-card decks are rushes, and the 3rd turn card advantage gained from using Entropy Animus will be quite worthless because you are already half dead. Most domin decks, being slower, have more than 30-cards so that decking out other domins is feasible. What Entropy Animus will affect the most, I reckon, are these domin decks (who already have low damage potential) and hourglass heavy decks that rely on key cards that can be stolen by Entropy Animus
"An added note, this card gives nightmare another use besides Ghostmare."
It does?
As you can see, I personally do not believe that this card is overpowered. However, if more and more people agree with your opinion, then I will change the card (it's better to be UP than to be OP).
The problem is that the mechanic can't really be nerfed without taking this card out of the Animi series. The units in which cards are stolen are the smallest possible ones. If cards are not stolen, it'd be more of an effect fit for Aether Animus, but I'm not too keen on changing both the mechanic and theme.