maybe Shaymin
Arceas
If by last Pokemon you mean the last one in the pokedex then that'd be Arceus, #493
go to the Pokemon league
Trade in a pokecenter, 2nd floor.
Pokemon diamond and pearl chocha culo teta bicho
Garchomp go in the Pokemon league the last trainer of it.
The last Gym is in Sunyshore City.
Beat the league
The last person (Cynthia) in the Pokemon league
Palkia, the one on the cover of Pearl.
at the sunny shore gym
On the 2nd floor of the Jubilife tv station