There is no possible way. If you use the 100% Pokedex fill, it will say that you have them all, but you really don't. There is a code for 999 Master Balls (way more then enough!). It's: 94000130 fcff0000
b21c4d28 0000000
b0000004 0000000
00000f4c 03e70001
d2000000 00000000
00000000 00000000 Hope that I helped! If I find one, I'll improve this answer!
ye you can
Catch trainer Pokemon
Mewthree cannot be caught in Pokemon Diamond, even with an Action Replay, because it does not exist in the game's data.
if its action replay than look up action replay codes on google
No you cannot.
You can't.
trade or migrate or action replay
not without an action replay and a Pokemon modifier code.
get an action replay, get the Pokemon modifier cheat for it, then catch all the Pokemon.
No, there is no legitimate Action Replay code for Mewthree for Pokemon Diamond.
you use the ds action replay or you migrate it
You can't unless you have an Action Replay Ds