But I just saw its base def and sp. def is only 58...
And how does one sweep entire teams?
Well the answer is Mirror coat, Encore and Counter. As soon as a pokemon switches in, Wubboffet can Encore then either counter or Mirror coat. If it is stat boosting, wubboffet switches and gives a sweeper time to K.O. and if it is a status he safeguards then switches.