Crobat

Crobat is a very cool Pokemon let down by unviable Atk and iffy moves. Crobat’s typing gives it 3 double resistances and potential access to a moveset effective against all 3 of these types. Unfortunately, it’s not up to snuff as a Flying-type attacker. It can be useful for early to mid game players who find a high-level Zubat and want to be more effective against Grass/Fighting type raids in particular, but its utility just isn't worth any meaningful investment.

In a gym lineup, Crobat can briefly annoy Machamp looking for a sweep. That's about all it does, though.

Best PvE Offensive Moveset

• Bite can be paired with Shadow Ball for effectiveness vs. Psychic and Ghost-types.

• Air Slash can be paired with Sludge Bomb to specialize against Fairy and Grass-types.

• Although Air Cutter has STAB, it’s an awful charge move.

• Ignore Return, as it can't deal Super Effective damage.

• Poison Fang is a bit too weak for PvE offense.

• Likewise, Cross Poison lacks damage output for offense. 

Best PvE Defensive Moveset

• Air Slash is the go-to defensive fast move, having STAB and more power than Bite.

• Cross Poison is slightly superior to Poison Fang as the 3-bar move of choice, but they're very similar for defense. 

• Sludge Bomb combines high power with an early damage window, but is used less frequently as a 2-bar move. 

• Shadow Ball can be seen coming from a mile away, but it nails Psychic-type counters if not dodged.

• Air Cutter is weak, fairly easy to dodge, and resisted by some of Crobat’s counters. However, it can deal some damage to Machamp, which is the main reason that Crobat should even be considered on defense.

Air Slash is a decent STAB Fast Attack and is generally the preferred option. Bite lacks STAB and energy gains, but provides strong Dark-type damage which is less likely to be resisted by Pokemon who counter Poison-types. 

Shadow Ball is generally recommended due to Crobat's other charge moves sharing the same Poison-typing, and is also useful to threaten Psychic-type counters. Sludge Bomb is strong and gets STAB, but doesn't provide additional coverage. Either Cross Poison or Poison Fang can be chosen as the secondary option for their low energy costs, enabling Crobat to bait shields while providing useful buff or debuff utilities.