Ultra Beasts are an interesting series of Pokemon. Some are beautiful like Nihilego and Pheromosa. Some are creepy like Zurkitree and Guzzlord. Some look pretty freaking cool like Kartana, Celesteela, and Naganadel. Buzzwole on the other hand can be summed up in one phrase:
I'M SEXY AND I KNOW IT
Steroid Mosquito
Ability: Beast Boost
Item: Leftovers/Life Orb/Big Root
Nature: Adamant (+Attack -Sp.Attack)
EVs: (HP 252) (Attack 252) (Defense 4)
Moves:
Bulk Up
Leech Life
Drain Punch/Close Combat
Darkest Lariant/Iron Head/Stone Edge/Ice Punch
Set Details:
A set up tank that recovers damage as it inflicts it. Bulk Up increases power output and bulk whilst making it easier to sweep and accrue attack boosts with Beast Boost, while Leech Life inflicts reliable damage and heals back some to keep Buzzwole in the game. Drain Punch also helps in this regard providing a secondary STAB that heals as it hits, but Close Combat will give you that extra oomf against sturdier targets at the cost of defenses. The last slot is up to what you fear most since 3 attacking moves won't hit everything for neutral damage. Darkest Lariat has the widest coverage and bypasses opponent defense boosts, Iron Head keeps Fairy types at bay, Stone Edge surprises Flying types that think they are safe against both STAB, and Ice Punch is there to handle the miscellaneous Dragon types. Pump EVs into HP and attack to make Buzzwole as tanky as possible, and your item choice is a matter of preference. Leftovers is consistent recovery, Life Orb increases power output and synergizes with the HP drain from Leech Life and Drain Punch, as does Big Root if you want to amp up your offensive recovery rate.
Can't Smack This
Ability: Beast Boost
Item: Choice Scarf
Nature: Jolly (+Speed -Sp.Attack)
EVs: (HP 4) (Attack 252) (Speed 252)
Moves:
Leech Life
Drain Punch/Close Combat
Darkest Lariant
Iron Head/Stone Edge/Ice Punch
Set Details:
Pretty sure every regular mosquito also hold Choice Scarves with how impossible they are to hit...Anyways, as above, so below. Same principle as the tank set only with max speed and attack investment along with a Choice Scarf. Pick an attack, knock out the opponent, and see if you can steam roll the opposition with each Beast Boost attack bonus.
If you have any other questions as to why you should put Buzzwole on your team, let me answer your question with another question...
WANNA SEE ME DRINK THIS GUY!?