Malicious Goons is a side quest in Final Fantasy VII Remake that you can complete during Chapter 14.
The quest can be started by speaking to Madam M outside her house in Wall Market.
Madam M says Corneo's Men are looking for Barret and they are heading toward's Aerith's house. Head to the place where you once fought Rude (just before Aerith's house in Sector 5 Residential Area).
Here you'll have to fight a Tonberry. These mobs are famous to the Final Fantasy Series and known for their one-hit KO attacks. In FF7R, they have similar attributes with moves like Doom and Gloom killing you in one hit.
Your best bet is to be constantly switching between characters, have plenty of Phoenix Down/Revives and try to get the fight done in quick time. Don't bother using Cure/Cura as the only moves Tonberry has are one-hit KOs and a binding ability.
Once you defeat the Tonberry, the Goons run off and you complete the quest.