One of my favorite gen 8 Pokemon, Flapple has a lot going on for it considering all the things it's design is inspired by. It's a worm in an apple, a pun on how worm and wyrm (A type of dragon) are homonyms, a clever nod to the falling apple that allowed Isaac Newton to understand gravity, and even a parallel to the serpent that tempted Adam and Eve in the Garden of Eden with the fruit of knowledge. The last comparison may be the most accurate at least in the competitive metagame since using Flapple seems akin to making a deal with the devil. Incredible offensive power at the cost of accuracy and coverage. But Flapple is still fun to use, apple skin and all.
Fruit of Power
Ability: Hustle
Item: Life Orb/Focus Sash
Nature: Jolly
EVs: (HP 4) (Attack 252) (Speed 252)
Moves:
Dragon Dance
Outrage
Grav Apple
Sucker Punch
Set Details:
Blistering power thanks to Hustle, but questionable accuracy and coverage. Boost attack and speed with Dragon Dance, sweep with Outrage and hope the opponent does not have a Fairy or Steel type in reserve, Grav Apple is your non-locked secondary STAB with a handy defense drop, and Sucker Punch serves as both coverage and priority against faster and frailer threats that still outpace you post dance. If you want to bypass Outrage's move lock and Hustle's accuracy drop, Dynamaxing is your best option and even lets you lay down Grassy Terrain with D-Max Grass thus boosting Grav Apple further. Don't bother with its G-Max form though since dropping your foe's evasion is not that useful since you will want to 1 hit KO your opponents anyways (Would have been a different story if G-Max Tartness boosted your accuracy though to compensate for Hustle). Life Orb boosts damage output, but Focus Sash can save your bacon since Flapple is not the sturdiest of targets. Invest everything into attack, but mostly speed.
Sin of Gluttony
Ability: Gluttony/Ripen
Item: Leichi Berry
Nature: Jolly
EVs: (HP 4) (Attack 252) (Speed 252)
Moves:
Dragon Dance
Outrage
Grav Apple
Sucker Punch/Acrobatics
Set Details:
Same set as above only without the accuracy drop or power of Hustle. Use Flapple's lower bulk to your advantage as once it gets below half health with Gluttony it will consume its held berry and obtain a power boost on par with Hustle only without the accuracy drop. Outrage again (Be mindful of Fairy and Steel types), Grav Apple is the more spamable move, Sucker Punch for coverage and priority, though Acrobatics is also an option once your berry is consumed and offers a speed boost when D-Maxed, and Dragon Dance compensates for poor speed and adds more power. If you are feeling particularly bold you could even opt for Ripen as your ability instead. The berry activation threshold will lower to 1/4, but you will get 2 attack boosts instead of one. But it's your call at the end of the day.
So give this literal dragon fruit a chance, and you may be surprised how far it will take you.