Going by stats, the overall best pokemon is Arceus.
the best place to catch a fire Pokemon in Pokemon platinum is fuego ironworks because you can catch a magmar which can evolve into magmortar with the magmerizer which is found on route 214
master ball
Arceus or Spiritomb. It depends on who your going to fight.
in etrena forest
Throw a masterball at it.
Master ball
Steelix
Darkrai
Bidoof.
best possible anser is action replay!
try your best to find spirtomb in Pokemon platinum
turtwig