I am running a GURPS Campaign. (Generic Universal Roleplaying System.) In the campaign, the players are detectives trying to solve various puzzles to stop a demon from coming forth.

I need some riddles for them to answer.

I need one in the form of a Catch-22 (a statement which contradicts itself), one in a question form. one in an actual puzzle form (such as one with a clock that's several minutes too fast or slow.) and one in standard riddle form. (Several lines.)

Can you guys help me with this?