A special Mewtwo is to be given away on wi-fi for... well, I don't think there's any particular reason. Here're the details.
Mewtwo: Lv. 70, Holding a King's Rock.
Normally Mewtwo learns Aura Sphere at lv. 100; doesn't really matter that it gets it 30 levels early, but that's still out of the norm so I noted of it.
More importantly, it gets the otherwise non-learnable Electro Ball. Electro Ball is basically Gyro Ball's opposite: the faster you are over your opponent, the more damage it does. However, while Mewtwo is fast, it actually isn't fast enough to make use of the move. Here's how it works.
Electro Ball starts at 60 Base Power; that's a third weaker than T-bolt, and only half as strong as Thunder. If the target's speed is between 33% and 50% of your Pokemon's, EB's Base Power goes up to 80. Still weaker than T-bolt, and most Pokemon either fall into this speed range or are faster than that when it comes to Ubers, so T-bolt and especially Thunder (it's main use is to counter Kyogre/Palkia in the rain anyways, so accuracy be damned) are just-plain better than Electro Ball.
If the target's speed is between 25% and 33% of your Pokemon's, Electro Ball gets 120 BP; the same as Thunder. You aren't going to fight Pokemon that slow unless they're a Tyranitar, a Ferrothorn, a Bronzong, etc. And for the former two, you've got Aura Sphere.
If the target's speed is 25% or less than your Pokemon's, EB gets 150 BP. That's definitely notable, but... You hit like three Pokemon in Ubers for the full BP, which is only 30 more than Thunder anyways. There might be one or two situations where EB is more useful than Thunder because of that 30 BP, but it just ain't worth replacing Thunder (and especially not any other move Mewtwo's got). EB on Mewtwo is even worse than V-Create of Rayquaza... =( C'mon Gamefreak, give us some broken event moves!
So yeah, another Poke for the srs collectors, nothing for competitive battlers to be concerned with... Unless you want to catch a Mewtwo with RNG abuse on BW or somethin'.