If he was a sickly green colour, they could call him MewSpew.
If he was overweight and wearing a poncho, they could call him MumuTwo.
If he was a cross-breed between Miltank and Mewtwo, we could call him MooTwo.
On the other hand, if he was a cross-breed between Noctowl and Mewtwo, he would be HooTwo.
If he was a soup-like beef dish, we could call him MewStew.
If there were five of them that sang and danced together, they could be Da MewCrew.
... okay, I'm done with the terrible jokes. I actually like the design, but I'm not particularly fond of the name MewThree, even though it makes sense for them to call him that. I know it's not official yet, so I'm hoping they'll come up with something that's catchy AND makes sense!