Seriously, NU's only clear suspect is Espeon. Anyone who denies this or tells me use *shaky* checks such as Slowking and Skuntank needs to play more NU. For straight up broken factor, run the sub Espeon set just to screw over Slowking and Skuntank, but a Sub+attack sets with entry hazards does just as fine.
About Magmortar, Ice-eyes raises a good point with Medicham. Honestly what CAN switch into this thing and live to tell the tale?!? It's like Magmortar, play*aroundable* but unlike Espeon they don't have blistering speed and have actually *checks*.