Crobat @ Black Sludge
Ability: Infiltrator
EVs: 44 Def / 252 SpA / 212 Spe
Modest Nature
-Brave Bird / Air Slash
-Roost / Taunt
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Heat Wave
-Nasty Plot / Roost
I know, I know, Crobat is laughed at in OU but I think that's exactly what makes him a worthwhile lure. No one expects Crobat to do anything save be a subpar Brave Bird spammer who can maybe have a Poison STAB on hold. Here we see a Special version of Crobat designed to lure not only Physically Defensive Skarmory but Ferrothorn, Forretress, and most other hazards/physical walls. Because Skarmory can easily handle Crobat's main moves and STABs it's a no-brainer to send in Skarmory when the opponent throws out Crobat because what can he do? Nasty Plot then one shot your ass with a Heat Wave, that's what.
+2 252+ SpA Crobat Heat Wave vs. 248 HP / 8 SpD Skarmory: 400-472 (120.1 - 141.7%) -- guaranteed OHKO
But of course, if the enemy sees you use a NP on the turn they switch then they'll suspect something's up so you can run Roost over Nasty Plot which cripples your damage but lets you keep the surprise Heat Wave:
252+ SpA Crobat Heat Wave vs. 248 HP / 8 SpD Skarmory: 202-238 (60.6 - 71.4%) -- guaranteed 2HKO after Leftovers recovery
I prefer the previous move set with NP so that if the opponent switches after sending in Skarmory you can still have a boosted attack for whichever pokemon they send in next.
As far as BB v AS it's a matter of how well you want to play the charade. Use Brave Bird to really lure the opponent into thinking you're running a typical physical Crobat or Air Slash if you don't care to play that high level of mind games.