I guess this is the sleep inducing crobat set you're searching for :
Crobat @ Leftovers
Nature : Timid
Ability : Inner Focus
EVs : 124 HP / 132 SpA / 252 Spe
-U-Turn / Roost
-Air Slash / Aerial Ace
The given EVs are designed to OHKO minimum HP Heracross with Air Slash. Max Speed is needed to outspeed Shaymin-S and tie with other Base 130s. If you opt for Aerial Ace, drop the Special Attack EVs, switch to a Jolly nature and put the leftover EVs into HP or Attack.