The Worst Ability

in my opinion, it's Truant.  It is Slakoth and Slaking's ability, and Durant's Hidden Ability.  What it does is make the Pokemon with it attack every other turn.  Yeah, LLLLLAAAAAMMMMMEEEEE.  The reason is that Slaking has amazing stats, and Norman, who has two of them, would hit harder than Groudon without Truant.  The cool thing is if you use Skill Swap, which switches abilities with the opponent, you can give Truant to the enemy.  Or, if the opponent has the ability Trace, which switches into the opponent's ability, then you can use it to make it even.