Talk to the mansion owner after you get the national pokedex
I think you use a round stone. I found the evolved version of hapinny in the wild;)
Hapinny
for hapinny to evolve into a chansey
hapinny into chansy
Give it an oval stone and level it up.
you will see hapinny in route 210
There is no rental Pokemon in in Pokemon platinum
You cant get Pokemon from Pokemon ranger to platinum!
how to get a togepi in Pokemon platinum
There is no grunt that you can give a Pokemon to in Pokemon platinum.
buy the Pokemon platinum book
yes there is a new Pokemon in Pokemon platinum. its name is Arcues.