In Diamond it is in the ruins with the Unknown, I am not sure about Platinum though.
Not that i know of, but the only one is inside Mt. Coronet or so... -KayserDragon
You can't.
The Odd Incense can be found in the Cerulean Cave along with Mewtwo himself.
in cerulean cave
at the cerulean cave
Breed Mr.mime while holding an odd incense
eat pie!
The item: Odd Incense increases all Psychic pokemon's attack by 20% while Mind Plate makes Arceus a Psychic Type. Why, even Twisted Spoon also does the same as Odd Incemse.
You can't. The Odd Keystone is only obtainable in Diamond, Pearl and Platinum. You will need to trade a Pokemon with an Odd Keystone to get it on SoulSilver.
there's a guy somewhere i don't remember and mining underground have u tried to use serebii.net?
You can get all the fossils underground, except for shieldon or cranidos. You find shieldon if your ID is even and Cranidos is your ID is odd.
U know the cave but not the spot? Have fun spelunking!