Poor Lopunny doesn't have much to work with anymore, being that it's Mega & strongest STAB move Return have been removed, but I think this set makes decent use of what it's got left!
Lopunny @ Toxic Orb
Ability: Klutz
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
• Fake Out
• Switcheroo
• Close Combat
• U-turn
Fake Out for first-turn flinch with the added bonus of STAB, Switcheroo to snag your opponent's item & badly poison them (which after the exclusion of Toxic as a TM/TR is a much more difficult thing to do), Close Combat for some solid damage (either to finish off a weakened/low Def Pokémon or just to make a good dent), and U-turn to get out of there & give your next Pokémon a nice head start against your opponent's while also negating Close Combat's defensive debuffs.
If your team doesn't really benefit from badly poisoning the opponent, you could run a different item that better suits your needs; Flame Orb for burn, Lagging Tail to cut Speed, Black Sludge for some residual damage, etc. And if you're not a fan of Switcheroo, you could use Thunder Wave or Teeter Dance instead; tack on whatever item you'd like & run Limber since Lopunny's main draw is its pretty good Speed.
Not the strongest out there, but if you're passionate about still using Lopunny despite its downgrades (like seriously, it doesn't even get Body Slam so it's best physical STAB is Headbutt) this might be the way to go!