I Know a Guy

In any situation (where it makes sense)
A PC can declare, "I know a guy," then
quickly outline that NPC & their
relationship. Fewer details are better.
Upon declaration, the NPC exists.
Then, when the PCs interact with the NPC,
the related player makes a Charisma roll
to see how the NPC reacts.
—
Advantage or Disadvantage may apply.