Feebas
With cheats
The rarest Pokemon is Dialga
there is no rarest Pokemon you have to train and train and including shinies there is no real rarest Pokemon at all.
The most rarest Pokemon card is original set kahangaskhan. Worth more then $1000 a piece.
mew2 is the rarest
The rarest Pokemon ever in my opinion is probably Arceus since it is so hard to get. I like most pies except pineapple or cherry.
No, you do not need cheats to get the rarest Pokemon. The only way to get the rarest Pokemon without cheating is to go to a Nintendo Event, held every few years or so, and download the rarest Pokemon there. Otherwise, you would need cheats to get the rarest Pokemon.
Pikman or Pokemon The Rarest is mewtwo
The rarest is stantler.
zekrom
By far, they have said Celebi is the hardest/rarest Pokemon to obtain outside of Japan.
That would have to be the Pokemon Arceus