Flying Monkey

Flying Monkey is an agent of a narcissist. They are enablers of narcissistic abuse. It is a Popular Psychology term

In the first place, the narcissist uses these third parties to gang up on the person they’ve targeted for abuse. Secondly, the narcissist may use a them to conduct a campaign of abuse by proxy.

They also come in handy when the narcissist is discrediting their victim. As a bystander, they provide independent confirmation of the narcissist’s scapegoat story.
Types of Flying Monkey
There are two kinds:

Benevolent
Malevolent

The thing that distinguishes the two is intent.

The benevolent ones are bystanders operating in good faith. They have likely been deceived into believing the narcissist’s scapegoat story.

Those of the malevolent variety willfully participate in the narcissist’s scheme in order to deliberately cause harm to the victim-survivor. They do this for a variety of reasons, i.e.malice,  envy, sadism, and to win the favor and approval of the narcissist.
Motivation
People who find themselves in the role of narcissist’s agent maybe be acting consciously or unconsciously. That is to say, a benevolent agents are unaware of the reality that they are acting on behalf of an abuser. While the malevolent agents are well aware of the true nature of the narcissist but participate for personal gain.
Origins of the term
The origin of the descriptor comes from the army of winged monkeys who carried out the orders of the Wicked Witch of the West in the book The Wonderful Wizard of Oz.