Pretty much any bulky Rock-type or speedy Psychic-type.
Aside from those stated above, Crobat has two major weaknesses: Stealth Rock and his awful defences. The trick to dealing with Crobat is not to outspeed, but to outlast. Good UU counters and checks to Crobat:
Mega Aggron – Meggron laughs at any Physical attacks Crobat throws at it, and Filter deals with Heat Wave variants. Crobat will likely U-Turn out, giving you a chance to Stealth Rock. In the rare case where it doesn't switch, a quick KO can be managed with Rock Slide/Stone Edge. EDIT: Heck, a Rock STAB isn't even needed.
[email protected] Aggronite
EVs: 252 HP / 136 Def / 120 SDef
- Heavy Slam
- Ice Punch/Rest
- Stealth Rock/Sleep Talk
0 Atk Mega Aggron Heavy Slam (120 BP) vs. 0 HP / 0 Def Crobat: 208-246 (66.8 - 79%) -- guaranteed 2HKO
252 Atk Choice Band Crobat Brave Bird vs. 252 HP / 136+ Def Mega Aggron: 46-55 (13.3 - 15.9%) -- possible 7HKO
It turns out that Heavy Slam hits Crobat just as hard as Stone Edge. Ice Punch/Stealth Rock is recommended over the standerd ResTalk in order to avoid Earthquake spam, which Crobat is immune to.
[Mega] Aerodactyl – Aerodactyl speed ties with Crobat and KOs with Stone Edge, while Mega Aerodactyl does pretty much the same thing, only it flat outspeeds at base 150.
[email protected] Aerodactylite
Ability: Tough Claws
EVs: 252 Spe / 252 Atk / 4 Def
- Stone Edge
- Sky Drop/Aerial Ace
- Roost/Ice Fang
252+ Atk Mega Aerodactyl Stone Edge vs. 0 HP / 0 Def Crobat: 444-524 (142.7 - 168.4%) -- guaranteed OHKO
252 Atk Choice Band Crobat Brave Bird vs. 0 HP / 4 Def Mega Aerodactyl: 130-153 (43.1 - 50.8%) -- 3.9% chance to 2HKO
Aerodactyl's calcs are the same as its Mega's, except Brave Bird becomes a garunteed 2HKO. In short, Crobat doesn't stand a chance.
Donphan – "Tee hee," giggles Donphan as Crobat's attacks bounce off of his tough hide. Speed don't matter with Donphan, priority Ice Shard kills.
[email protected] Assault Vest
EVs: 252 Def / 172 HP / 84 Spe
- Rapid Spin
- Ice Shard
- Knock Off
252+ Atk Donphan Ice Shard vs. 0 HP / 0 Def Crobat: 110-130 (35.3 - 41.8%) -- guaranteed 3HKO
252 Atk Choice Band Crobat Brave Bird vs. 252 HP / 252 Def Donphan: 160-189 (41.6 - 49.2%) -- guaranteed 3HKO
Donphan comes this close to losing to Crobat, but with the combonation of recoil and Kce Shard priority, Donphan is the victor.
Hippowdon – Crobat can hardly scratch Hippowdon's immense bulk, and his puny Brave Birds and Cross Poisons ping off of Hippowdon like arrrows off a stone wall. Slack Off remedies damage taken from crits, and Rock Slide murders Crobat. Hippowdon can also set up Stealth Rock and phaze wih Whirlwind.
[email protected] Leftovers
Ability: Sand Stream
EVs: 252 HP / 252 Def / 4 SDef
- Steath Rock
- Slack Off
- Rock Slide/Stone Edge/Ice Fang
0 Atk Hippowdon Rock Slide vs. 0 HP / 0 Def Crobat: 144-170 (46.3 - 54.6%) -- 98% chance to 2HKO after sandstorm damage
252 Atk Choice Band Crobat Brave Bird vs. 252 HP / 252+ Def Hippowdon: 147-174 (35 - 41.4%) -- 72.1% chance to 3HKO after Leftovers recovery
While Hippowdon cannot OHKO Crobat without any Attack investment, it still manages to kill Bats before it can do anything. Most likely, however, Crobat will U-Turn out (13.5 - 16.1%) and just be ripped apart by SR.