Beautifly

Swarm
Boosts power of Bug moves 50% when at 1/3 HP or less.
Tier: UU
Statistics
Min- Min Max Max+
HP
60
- 261 324 -
Atk
70
158 176 239 262
Def
50
122 136 199 218
SpA
90
194 216 279 306
SpD
50
122 136 199 218
Spe
65
149 166 229 251
Name Item Nature

Choice Specs

Choice Specs Timid
Moveset EVs
~ Bug Buzz
~ Shadow Ball
~ Psychic
~ Energy Ball / Hidden Power Ground
6 HP / 252 SpA / 252 Spe

Beautifly has only one stat remotely resembling "decent" and that's Special Attack, so try this if you want it to do any damage at all. Hidden Power Ground is mostly for Mawile and other Steels Beautifly may run into.

Name Item Nature

Stun Spore

Leftovers / Focus Sash Modest
Moveset EVs
~ Bug Buzz
~ Shadow Ball
~ Stun Spore
~ U-turn / Psychic
252 HP / 6 Def / 252 SpA

Paralyze anything you can with Stun Spore and attempt to hurt stuff with Bug Buzz. Shadow Ball hits Rotom and Banette, while Psychic helps against Poison-types like Swalot. U-turn can give Beautifly a free, weak hit against a paralyzed foe, or scout for others.

Other Options

Nothing really, Beautifly is way too fragile to attempt Roost or Whirlwind.

EVs

Max Speed and Special Attack for the Choice Specs set. Max out HP and Special Attack on the Stun Spore set.

Opinion

It isn't the worst Bug-type around, but it is pretty close. Stun Spore and a usable Special Attack stat are the only positive things about Beautifly, which are worth very little when it dies so easily.

Counters

Rotom resists Bug Buzz and easily KOs with Thunderbolt, but watch out for Choice Specs Shadow Ball. Any of the NU/UU Steel-types can take it quite easily. Just take advantage of its many weaknesses and terrible defenses; it'll die in no time at all. Stealth Rock strips it of 50% of its HP, so if you've got that on your side, Beautifly will be even easier to take down than it already is.