After getting rid of the ReGalactic grunts taking over the Valley Windworks, you've resumed your trip to Eterna City. The next stop is Eterna Forest, which is sandwiched in the middle of Route 205. The Old Chateau is still standing and so's the Moss Rock, believe it or not. All wild encounters are the same as in Platinum except Murkrow and Misdreavus have been added to the encounter table here. Slakoth, Caterpie, Weedle, Seedot, Pineco, and Nincada have also been inhabiting this forest alongside their new friends Karrablast, Shelmet, Sewaddle, Scatterbug and Grubbin.
The way to the Old Chateau is blocked off by small plants, so you'll need the Hidden Move for Cut from Gardenia first after winning against her in a gym battle. And just so you know, any HM you learn is registered to the Hidden Moves app on your Poketch to avoid ruining your Pokemon's movesets as a wild Pokemon will be summoned instead to perform the moves.
The HM moves are as follows: Cut and Rock Smash for Bidoof... Fly and Defog for Staraptor... and finally Strength, Surf, Waterfall, and Rock Climb for Bibarel.
So, what will you do to prepare for the next gym battle in Eterna City? It's up to you!