Going through my handy dandy list of Pokémon that aren't in the Kalos Dex, the only single stagers that remain for the possible spots in Coastal and Mountain Dex are(ignoring the legendaries, of course);
Unown
Girafarig
Corsola
Stantler
Shuckle
Spinda
Castform
Tropius
Spiritomb
Rotom
Maractus
Bouffalant
Unown and Rotom are unlikely as Unown generally has a specific location whereas Rotom is generally found post-E4. As for the others, Corsola is extremely likely because it is the best fitting for Coastal Dex, but Shuckle is rather unlikely because Carbink is essentially itself, and Shuckle is found in coastal areas(unless of course, it is the remaining spot in Coastal Dex, in which case Corsola gets the cut). Bouffalant and Spinda are both commonly found in mountain areas, so they are the likeliest shots, but Spinda is rather debatable because of the whole "Hoenn Confirmed" thing.
Also, in addition to Druddigon being listed twice in the Mega Evolution list, Banette's spelling error should be fixed as well.
Edit: OK, the former is corrected apparently.
Edit 2: Forgot Maractus.