Plecosy

Plecosy is the evolved form of koish it was one the first rebooted catchymon created it evolves from koish at level 30 then it evolves into Snowking at level 100 then you can mega evolve it using the Snownite X or Y.

You can get a plecosy from Miv the water/ice type gym leader when you beat her and she will also give you a Fishe,Arrogar,Trilomite,and Slee.