There is no "entrance" you must get the explorer kit from the digging man in Enterna City (his house is beside the Pokemon center) then just use it outside!
You can find the fire stone in: Fuego Ironworks Solaceon Ruins (by using the dowsing machine) The Sinnoh underground
yes but sinnoh
you have to see all the Pokemon in sinnoh
yes
Its Phione in Pokemon Platinum, You can get it by breeding a Manaphy and a Ditto Actually; Rotom comes after Manaphy in the Platinum pokedex. Kthnx. http://pokemon.marriland.com/platinum/pokedex/list/sinnoh/ Rotom comes after manaphy in the platinum pokedex phione can be made by breeding a manaphy and a ditto but he's actuelly not in the platinum pokedex :D
First you must have an explorer kit whitch you get in eterna city and then you go underground and dig until you find a fossil.
All i know is how to get it in pearl platinum and diamond if you asking for that in sinnoh underground but otherwise i dont know.
Travel the Sinnoh region and collect them. The other way to get some plates is digging underground.
You can find the fire stone in: Fuego Ironworks Solaceon Ruins (by using the dowsing machine) The Sinnoh underground
Wild Clefa, Clefairy and Lunatone have 5% chance to hold it, you can dig in Sinnoh Underground or trade with someone.
pelipper is the 120th Pokemon in the platinum sinnoh dex.
You can't. Sinnoh is only available in Pokemon Diamond, Pearl and Platinum versions which are set in sinnoh.
mossdeep is not in sinnoh
No.
Swinub is #203 in the Sinnoh Dex in Pokémon Platinum.
It has only the sinnoh region.
in sinnoh 210