you can't.
Breed a Loudred and hatch the Egg
You can't find a Whismer walking around.
Whismur is #293 in the national pokedex, and it is a Normal type Pokemon.
It depends. Whismur is a Normal pokemon, maybe Normal/Ground. All I really know is if Whismurs are good now, they'll be really, really good when then evolve into Loudred, and more so when they are Exploud. But, not considering evolution, is Whismur good? Each pokemon has its own special potential, but I guess if Whismur is good depends on the trainer. Are you a good Trainer? If so, yeah. Whismur's good.
you can't.
You can find whismur at route 503, and mankey is currently a swarm pokemon, so you'll have to wait or trade for it.
Breed a Loudred and hatch the Egg
You can't find a Whismer walking around.
go to route 20
You cannot snag a legit whismur in Pokemon XD, only trade to Pokemon XD from another game.
Whismur evolves into Loudred at level 20.
With a pokaball
buy the Pokemon platinum book
Whismur is #293 in the national pokedex, and it is a Normal type Pokemon.
The 151st Pokemon is Mew and is unobtainable in Pokemon Platinum.
no you can't find a torchic egg in Pokemon platinum