Whenever Arthur defeats one of the trustees, it's usually awesome one way or another.
* Arthur and Suzy defeat Mr Monday by having Suzy [[HoistByHisOwnPetard write on him to attract the ire of his own bibliophages]]
* against Grim Tuesday, he wins the Second key in a contest of creating art, by playing a tune he wrote as a child on a xylophone.
* When Lady Friday's trap opens a hole into Nothing, Arthur manages to close it using the power of all four of the keys he has so far. He didn't even have them with him at the time, he just summoned them all from halfway accross the house.
** Arthur's 'Keys! Bring her to me!' moment in ''Lady Friday'' comes to mind. It's a brief display of just how powerful Arthur is by this point.