What is the rarest Pokémon on Pokémon Diamond?

Answer 1

The rarest Pokemon in Pokemon Diamond are the Pokemon you can not get in

Pokemon Diamond, such as the Kanto, Johto, and Hoenn starter Pokemon (Bulbasaur,

Cyndaquil, Mudkip, etc.), legionaries [Lugia, Ho-oh (Event Pokemon such as Deoxys

aren't really rare), etc.], etc. Pokemon that are migrated from Pokemon GBA games are

also rare Pokemon in Pokemon Diamond.

Hope this helped!

-Pyrenix

three words mewtwo and mew

The true hardest Pokemon to catch are: Deoxys, Mew, Celebi, Jirachi, darkrai, shaymin, Ho-oh and lugia

that is because they are event Pokemon and the events are over, so to get them you need cheats, or trade them with someone who has, and they may not give them up easily.