Since the GFaqs topic was closed, wasn't sure if I was supposed to post here or not.
Milotic @ Leftovers
Calm - 212 HP, 100 Def, 196 SpDef
Marvel Scale
~Mirror Coat
~Recover
~Surf
~Ice Beam / Dragon Pulse / Toxic
Slight spin on the Mirror Coating Milotic - anything with a half decent special attack will take tons of damage even though you're stacking up the SpDef. I prefer to switch this guy in on Thunder Wave or Will-o-wisp for a defense boost (or even if your opponent has put down one layer of Toxic Spikes...). The SpDef EVs allow you to survive plenty of Nasty Plotters, although I think you're SOL with LO Infernape's Grass Knot.