Crobat @ metronome ("flying up high" should count as a successful use so you should get a free 10% boost each time fly hits an opponent)
EVs: 100 Atk
- fly
- cross poison
- screech/X-scissor/zen headbutt
- screech/X-scissor/zen headbutt
This Pokemon is obtainable very early and ends up with okay physical attack. If you catch the level 3 Zubat in Ravaged Path, it'll probably evolve into Crobat around the time you battle Maylene. After fully evolving, it unfortunately still has less physical attack (and less useful coverage moves) than some of your other options, and it doesn't learn any attack-boosting moves (without breeding).
Gliscor @ expert belt/earth plate/soft sand
Ability: hyper cutter
EVs: 100 Spe
- earthquake
- swords dance
- aerial ace
- ice fang/stone edge
This Pokemon learns swords dance, and its physical defense, speed, and defensive typing all make it easier to set up a sweep. Its offensive typing and coverage moves let it do super effective damage against a lot of opponents. It does need the earthquake TM to work, so the rest of your team has to either give up ground coverage or use a weaker move like dig.
Gyarados @ mystic water/splash plate/metronome
EVs: 100 Atk
- waterfall
- dragon dance
- ice fang
- return/earthquake
Gyarados's high physical attack, solid offensive and defensive typing, and dragon dance make it one of the best Pokemon in the game. Unfortunately, it learns only one flying attack, which is post-game exclusive. If you use Gyarados, be sure to catch a Magikarp with a good rod (try to get one between level 15 and 22) so you don't need to exp. share train it for like 10 levels.
Scyther @ silver powder/insect plate/metronome/sky plate
Ability: technician
EVs: 100 Spe
- aerial ace
- swords dance
- X-scissor
- brick break
This is another powerful swords dance user. Scyther's offensive typing isn't great and it has 5 weaknesses, but it also has high physical attack and speed and a good ability. If you use Scyther, buy a swords dance TM, as it's pretty cheap and lets Scyther learn the move a lot earlier.