This is best to use when you’ve just finished a party. A buddy of mine called it “The Rosencrantz & Guildenstern Game.” The ven called it “The Midnight Game.”
When the nobles go to bed, the servants come out to play. Their masters and ladies are all asleep (or pretending to be asleep) and that affords the servant class an opportunity to let down their hair.
Nearly every lord or lady has a maid or valet. (Even if they don’t have the Vassal; that just means your maid or valet isn’t cool enough yet.) Write down your maid or valet’s name and throw all those names at the GM. Then, the GM throws all those names in a hat and everybody draws one. If you draw your own, throw it back and pick another.
For the next game session, you play a maid or valet to one of the other nobles. Moving around the house by candlelight, meeting with other servants for less-than-honorable purposes, spying on other nobles, carrying out illicit affairs.
Spend a whole game session on the vassals. If your GM is generous, he may even allow you to elevate a vassal to NPC status. If you are all very good.
I mean bad. Very, very bad.