I was in a Pokémon battle and had used Mean Look with Umbreon and Baton Passed a couple of times, and after a lot of battling (without switching out except via Baton Pass), the opponent was eventually able to switch out. Does anyone know why this happened/when Mean Look's effect wears off?
If you use Mean Look, the effect is not kept when you use Baton Pass. Before Generation IV though, it would have been Baton Passed to your Ursaring as you would have expected. Other than that it doesn't wear off on it's own unless the opponent forces itself to switch out.
Mean Look lasts the entire battle until the Mean Looked Pokemon comes out of battle, if by fainting, switching out etc.. If the user uses a move that switches itself out however, like Baton Pass, Roar and Whirlwind, Mean Look will be in effect on the newly switched-out Pokemon. Past Gen V though, moves like this disabled the effects of Mean Look.
Hope I helped. :)