The mission is essentially a non-mission where the only actions are to first accept the mission, then to turn it in. Shortly after the mission is taken, Sir Reginald utters his riddle, before promptly being squashed by a huge die.
"In case you're wondering, the answer starts with a "D" and and rhymes with "Sharkman"."
Turn In: Die
The narration indicates that the die represents a die that Brick uses to crush a Sir Reginald playing piece on the game board.
The riddle spoken is a quote from the 1990 movie, Darkman, said by the titular character at the end of the movie.