Beautifly

Swarm
Boosts power of Bug moves 50% when at 1/3 HP or less.
Type Tier
Bug / Flying NU
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

Paralyzer

Leftovers Timid / Jolly
Moveset EVs
~ Stun Spore
~ Substitute
~ Morning Sun
~ Hidden Power Bug / Hidden Power Flying / Giga Drain / Psychic
252 Atk / 252 Spe

Bug Types tend to suck and Beautifly is no exception, actually it's the third worst bug Pokémon, after Shuckle and Beautifly's cousin Dustox. Stun Spore something, and if you aren't dead, use Substitute until your opponent switches or is fully Paralyzed, or you can't use it anymore. If your opponent switches, Stun Spore the next Pokémon, otherwise attack. Dies pretty easily but it's the best thing it can do.

Other Options

Shadow Ball for surprising Ghosts maybe, Thief because stealing an item is more or less the best thing Beautifly do. Silver Wind and Aerial Ace are options over Hidden Power Bug and Hidden Power Flying respectively.

EVs

Just max out Attack/Special Attack and Speed and give it a Timid/Jolly nature, because it absolutely won't last long.

Opinion

Don't use it, I just did that analysis because no one else would. Or you can use it on NU teams, 90 Special Attack isn't that bad. Beautifly is begging for Sleep Powder, damn Nintendo.

Counters

Basically, every move with more than 60 power, and that is not named Earthquake, OHKOs Beautifly. You'll want to hit it first because it will Stun Spore you. If you have a Guts user, just switch it in.