I'm positive this Mew is hacked, based mostly on the fact it came through GTS. No valid event Mew can be traded on the GTS, due to the ribbons that many Mews hold. There were a few Pokemon Ranch Mews that didn't have ribbons, but those are level 50, while yours is level 10.
There were generation 3 Mews that didn't hold ribbons either, but your location doesn't specify any Mew that was given without a ribbon. There were three event Mews that did originate from "a lovely place," but those three were all level 100, while yours is, again, level 10.
As the other post said, no Mew was ever given out in a Level Ball either.
The ID Number is also off. No Mew was given out with that ID number specifically. The only Mew without a set ID number is the Faraway Island Mew in generation 3, but as the location and level says, this Mew did not come from there.
The fact it has Pokerus doesn't mean its hacked, but it certainly should raise suspicion.
Ability and nature are valid. The moveset is also valid even for a hacked Mew I guess. Sorry to say this too, but those stats look like they all have 0 IVs (i.e. they're the lowest they could possibly be). Although at level 10 and with no EVs, its hard to tell. If you plug them into an IV calculator, you get 0-9 in all stats (if it has no EVs).
Main source: http://www.serebii.net/events/dex/151.shtml
Because this Mew is hacked the way it is, it should not break anything in your game. Hacked Pokemon, in general, won't break anything unless they are an invalid Dex ID number (numbers ranging from around 722 to 65535 iirc). Even if this Mew somehow was an invalid ID number as well, I'm confident Nintendo coded the GTS to prevent these IDs from being traded to someone.
Hope this helps. Sorry for the bad news. :(