... Wynaut, and I guess by extension the Wobbuffet.
Don't get me wrong. I'll be the first in my house to tell you that I love Wobbuffet to friggen DEATH *hugs Wobby* but hoollly crap, leveling up Wynaut to get Wobbuffet to eventually get to level 40 so I can shadow tag certain roaming Pokemon....
It's a pain in the BUTT trying to predict what attacks the foe is going to use. For example, I'm leveling up my Wynaut, and I'm up against a Meowth that knows Scratch, Growl, Bite, and maybe one other attack I haven't seen used yet...
And what happens? I go for Counter against Scratch, Growl is used. I use Counter again, it uses Bite (super effective, augh!). I use Mirror Coat, it uses Growl, and then Scratch, and... this goes on until either Wynaut faints, I get lucky with a hit, or I flee from battle. ; ;
Summation: Leveling up Wynaut is friggen haaaarrrrd and irritating!