Q: Can you use the Skullduggery promo card to cancel a Plunder – not on the Rule itself, but on a single act of Plundering?

Or to cancel City Of Thieves in Adventure Time Fluxx, or Fantasy Fluxx, or Crime Happens in Batman Fluxx, or Acquisition in Star Trek: TNG Fluxx

A: Yes.

(Note that if you stop Acquisition from happening, you don’t get to take a card from the Acquiring players hand either. The entire card play is canceled.)