An ability that acts as if the Pokemon it's facing has no item. Kind of like Unnerve.
8/10, it would be consistently useful and maybe even be a game changer against certain opponents.
How about an ability that summons clear weather?
EDIT: Ninja'd. I give the post actually above mine 7.5/10, it could be useful but maybe not something to count on.
Isn't there an ability that already does that? Or makes the Pokemon not phased by it at least? If not, it would make sense and I'm surprised there isn't one already. 8/10, since I don't care for weather changes much anywho xP.
Antagonist - Automatic Taunt effect for adjacent Pokemon as long as the Pokemon with Antagonist is in battle. Should be reserved for relatively frail, mischevious looking pokemon like Glalie, Weavile or Electivire.
Walk away from your Wifi to DC without penalty. It's fun!