So I have a Japanese ampibom in diamond and I have it in white 2 now so I'm wondering if masuda method would still work
The Masuda method describes a way to obtain Shiny Pokémon more easily from Generation IV onwards. It occurs whenever Pokémon of differing language are bred.
I don't see anything about transferring in there. source
Yes it does. Because even though you're moving to another game. You still have it Japanese. It's like having a Japanese Pokemon from "gts" "Wondertrade" and all that other stuff. . :') hope you understood.