I can't run Crobat as an attacker. I have before
mentioned Crobat as a defensive type before. Here's my moveset that takes advantage of speed and defenses:
Crobat @ Focus Sash
Timid
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Taunt
Hypnosis
Roost
Air Slash
This is my current lead pokemon. Hypnosis is the default behavior of Crobat, while taunt prevents lead set-up pokemon from doing what they do. With the above defense EVs, I can survive hits on the Defense side... not so much on the Special Side. So in Jolteon vs Crobat leads, I want two chances at hypnosis before switching out.
When the set-up pokemon switches out because of taunt, hypnosis their sweeper. Crobat can stay in and air slash on the second turn if you want to play conservative. Few pokemon are faster than Crobat, and that Focus Sash is still there for his protection.
In the late game, Crobat serves as my Heracross / Breloom counter. Breloom can't do anything but spore Crobat, and the above EVs make Crobat a 3-hit KO to Adamant Life-Orb Breloom Focus Punch. Without Life Orb, Breloom Focus Punch drops down to a 4 or 5 hit KO. (Gotta love 4x resists). Switch on the Focus Punch, Taunt if Sleep Clause isn't in effect (either no sleepers or whatever) to prevent spore. Roost off the damage, break the sub and kill with Air Slash.
Heracross is dangerous with Stone Edge, but most of the time he defaults to Megahorn and Close Combat, which is 4x resisted to Crobat and he can easily roost off the damage. Both Heracross and Breloom are 4x weak to Air Slash... though I'm not exactly sure if it is a OHKO.