No, there isn't. The only way possible is to hack the ROM and import Mewthree into the game.
Here's the fact..MEWTHREE DOES NOT EXIST!!There are only 435 Pokemon at the moment, and they're all known.There is no way to get "him" even with cheats, because he isn't in the game.
there is no way. cheating is the only way
no
In Pokemon Diamond and Pokemon Pearl, there is no possible way to catch a Giritina. You can, however, either catch one in Pokemon Platinum or trade with someone who does have one. In Pokemon Pearl, you catch Palkia at Spear Pillar. In Pokemon Diamond, you catch Dialga at Spear Pillar.
In a way. In pearl, you catch palkia. And in diamond, you catch dialga.
You can't catch Murkrow in Pearl. Murkrow is a Diamond-only Pokemon. Just like Misdreavus is a Pearl-only Pokemon.
There is no way to obtain Mewthree since it doesn't exist.
Mewthree is not a real Pokemon in the Pokemon series of games or shows. It is a fan-made Pokemon.
no way!
The only way to catch either one of them would be to transfer from an other game, since they aren't found in Pokemon pearl.
Catch all the Pokemon.
you can do it by cheating but that is the only way