Seismitoad is presen-Aw heck I'm revealing it all anyways so...
Accelgor-(ties in with N's Escavalier)
Seismitoad-Rain Dancer
Ferrothorn-Not so weak in rain, entry hazard
Genescect-Douse Drive fun
Hydreigon-Surf in rain
Heatmor-Because no other major NPC uses him.
the way I have the gyms and rival teams set up is similar to DPt, you see all the Unova Pokemon to complete the dex at game's end, so GL, Rivals and E4 showcase the harder to find ones.