Just defeat the elite 4 again and he will return.Hope it works.
Yes, Mewtwo will reappear once you have defeated it however you must defeat Lance, the Champion after defeating Mewtwo in order to regenerate it.
you cant catch mewtwo in Pokemon platinum peral diamond you can in Pokemon heart gold and solsilver in canalave cave
you finish the game with heart gold then you go to kanto and you defeat gyms and on the way you'll get zapdos moltres mew mewtwo an so on
You can beat the Elite 4 the 2nd time, do Gym Leader Rematches, More Legendary Pokemon, the new area's you can visit, beat Clair and Lance at Dragons Den, Do a Rival Battle at the Indigo Plateau
just defeat blue, the 8th gym leader
mewtwo
Mew can't be catched in Pokemon heartgold, only mewtwo.
U can't in heart gold but u can catch mewtwo
That's just an fan-made sprite. It doesn't really exist in the real games.
he goes to sinnoh
yes after you beat them you can defeat ash, his Pokemon are level 80, after you defeat him then you can go to a whole another region! Johto
Get the S.S. Aqua Ticket from Prof. Elm and go to Olivine City. Take the boat to Kanto and battle all the Gym Leaders!