Question

What is the best nature for Noivern?

Answer 1

Since Noivern's highest stat is its speed, I'd go with Timid (+S -A). Also, (mentioned by sumwun in the comments), even though it's fast, it still isn't fast enough and gets outsped by other Pokémon faster than it.

Comments

Other natures your Noivern could have: Hasty(+S -D), Jolly(+S -SA), Naïve(+S -SD), or Serious(+-S).

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Noivern doesn't need Speed.

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Noivern still gets outsped by some stuff. Of course it needs speed.

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That's just like saying Pheromosa needs Speed. Pheromosa already has too much and has better stats to use on. We need to focus on it's main system, attacking. Raise it's Sp. Atk.

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A choice specs Noivern with 252 SpA EVs will already one-shot most non-fairy Pokemon with either draco meteor or heat wave. It's more likely to get outsped than tanked, so it need speed more than it needs special attack.

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Or just use

Noivern @ Choice Scarf  
Ability: Frisk  
EVs: 252 SpA / 4 SpD / 252 Spe  
Timid Nature  
IVs: 0 Atk  
- Boomburst  
- Dragon Pulse  
- Air Slash  
- Flamethrower

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Choice scarf is bad on Noivern because it needs choice specs to break through certain threats. Because substitutes are quite common, infiltrator is almost always better than frisk.

Answer 2

Timid or modest works, but if your going for a scarf item I would go with the other stat that isn't boosted. For ex: choice scarf: modest, choice specs: timid

Comments

Choice scarf is almost always worse than choice specs because it needs the special attack to break through certain threats.