Shadow Venomoth

In a sea of Bug-types vying for stardust, none of them that outstanding to begin with, Venomoth doesn't bring much to the table. Its dual-typing allows it to double-resist FIghting types, and its moveset gives it the tools to hit them super-effectively, but its stats are just too low to make a splash in this regard; especially in the face of other easy-to-obtain options like Alakazam or Espeon. It's somewhat adequate if you need a Bug-type, but Bug-type is fairly low priority for most trainers as anything that Bug counters can generally be countered better by another type outside of double-weaknesses. On defense, Venomoth has the aforementioned advantage of double-resisting Fighting types and hitting back hard with Confusion, which is a good quality given the ubiquitous nature of Machamp, but it doesn't have much else to its benefit

Venomoth can help get a trainer through the early stages of the game, but it's not a wise long-term investment.

Best PvE Offensive Moveset

• Bug Bite and Infestation are somewhat similar, with the former having higher base damage and the later higher energy gain, but Bug Bite pulls ahead slightly by being easier to dodge with and having slightly lower overall average damage, although it is a legacy move.
• Confusion is an objectively great move, but its performance isn't objectively great on Venomoth.
• Bug Buzz is Venomoth's charged move of choice, trumping Silver Wind and giving it a dual-bug moveset with Bug Bite or Infestation.
• Psychic can be paired with Confusion if you're desperate for a Psychic attacker, though this really isn't the Pokemon to do this with. 
• Poison Fang is not a good move for Venomoth.

Best PvE Defensive Moveset

• Confusion is Venomoth's best defensive quick-move due to its sheer power.
• Infestation is an acceptable defensive move.
• Bug Bite falls behind on defense, and is the worst option for a quick move.
• Silver Wind has multiple bars and hits fairly hard, making it the best charged move.
• Psychic can hit Machamp fairly hard.
• Poison Fang has 3 bars and STAB, but its low base damage makes it a fairly poor move on defense.

Confusion is more or less what gives Venomoth its niche. Infestation provides superior energy generation, but Venomoth's charge moves are rather lackluster. 

Poison Fang costs the least amount of energy, benefits from STAB, and can be used frequently. Bug Buzz and Psychic both cost large amounts of energy, with the former benefiting from STAB, while the latter provides more Psychic-type coverage.