*blows dust off of game cartridge* Okay, let's see what I have...
I think that the normal ones are legit, but the legendaries and mythicals are hacked/illegal. I'm rather attached to some of them, though, so I might not be willing to sell/trade them.
So they are illegal but still tradeable. Not as in the case of a shiny Hoopa, which I really wanted but learned that it was 100% illegal and shiny locked and couldn't be traded. ;-;
I believe that most of them are hacked but they can be traded. I received all of them through trading with other players or through wonder trade. I don't know if they can be placed in the GTS or not.