This card is just amazing, although I don't see it as OP.
It's very fun to use, like others in this thread have already commented on. But a little note to Jelly, if you honestly want to copy a creature, just use TU, as the Duality+RT combo is an extra card for less bonus (Unless of course you get multiple copies, but you've still got to pay for them all) but that may be offset by the fact that RT provides control as well.
A little side note: If a deck with Mind Gate comes up against a mono-Aether with less cards (Or one that lost the coin toss) it'll win because it has more shields.
I need to test this card out some more though, like Dema said it could go in well with stalling FG decks, they usually have useful cards (Getting Purify against Scorpio would be nice, or a few Firestorms on Eternal Phoenix/Graviton).