If by last Pokemon you mean the last one in the pokedex then that'd be Arceus, #493
Arceas
go to the Pokemon league
maybe Shaymin
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
In Sunnyshore city same as pearl/diamond.
If your talking about Ponyta then level 41