'Flying monkeys' (from The Wizard of Oz) are the people a narcissistic person recruits — knowingly or not — to pressure, guilt, spy on, or punish you on their behalf: relatives urging you to 'just apologize,' mutual friends reporting back, new partners repeating old smears. Most aren't evil; they've only heard one side, persuasively told.
The narcissistic person gets there first with a sympathetic story in which they're the victim and you're unstable, cruel, or crazy. Helpers then apply pressure believing they're doing good. This is why your explanations to them so often bounce off — they came pre-inoculated.