Want the other fossil/a ditto?
I'm not sure if you have to defeat the Elite Four first or not, but I think it's a pretty safe bet you need to have already chosen your fossil out of Mirage Tower in the desert on Route 111. Between the Root and Claw fossils, if you get one, you probably assumed you couldn't get the other, so you chose carefully. To get the other:
Go to Fallarbor Town- do you remember the house where you got the TM for Dig? That house- the Fossil Maniac's House.
He'll be standing away from the wall. When you try to walk past, him, he will advise you not to go back there, but go back there anyway.
Go through the door; you are now in the "Desert Underpass", I believe it's called.
In this underpass, you will run into wild Whismur, Loudred, and Ditto, all around the same level as the wild Pokémon on Victory Road (high 30's-low 40's). Perfect opportunity to catch a ditto, as they are rather common in this little underground path.
Keep going to the right- it's really only one path, you don't have to worry about getting lost. After a while, there will be a patch of sand right above you (ignore it, there's nothing there) and a patch of sand in front of you. When you reach this patch of sand, you will find the fossil that dropped down and disappeared into the desert.
Thank you, hope it's helpful!
And, for reference's sake, I tried this myself or I wouldn't post it! It works!
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