Help finding that one Pokemon

[ForsakenM~]

So, I'm going through each route and catching all the Pokemon I missed, but I'm currently stuck on Route 117.

I'm at the 'Nearly Complete' state in which I only need one more Pokemon in that area.

I've got Azumarill, Corphish, Deerling, Goldeen, Illumise, Magikarp, Marill, Masquerain, Oddish, Rattata, Roselia, Surskit, Tympole, Volbeat, and Zigzagoon.

Hit me up if you know who it is, and if I can encounter it easier somewhere else!