140 HP, Fighting Weakness, and 3 Retreat Cost seems average on a Stage 2, considering Blastoise and Charizard are like this. That Fighting Weakness will be abused a lot, sadly....
His Ability, Dual Brains, is far stronger than some people here are giving credit for.
You forget that we are getting a seriously disruptive Supporter, Ghetsis, at some point, and Dual Brains will make him extremely easy to get, because you retrieve him with Skyla. Guaranteed Ghetsis on Turn 2 is pretty damn smart. Also, being able to play 2 Supporter in one turn opens up the possibility of getting two Stage 2 Pokemon (same or different) onto the field in one turn! Think of how you've reduced your opponent to just an ordinary shmo when you shuffle in all his Item Cards, and then lock his Supporters with Stoutland BCR! Its still exquisitely seasoned Landorus EX bait, though...
Even so, that potential Deck still fares greatly against many other Decks in the format. Mewtwo EX only needs Energy to deal big attacks, after all. This card definitly opens doors to tricky combos we've never considered due to the game's own limitations, and for that, I give him an 8/10.
His single attack, Gyro Ball is fair, but Magnezone benefits you far more with his supportive Ability on the bench.