The riddle for one of the Wraith Hearts talks about the combination of the treasure chest being in the book. Look inside the instruction book of the game and you will see the three characters that stand beside the treasure chest and the combination for the chest is right around them.
Super moves are available once your super bar at the top is full. To build that meter quickly, tap X rapidly and repeatedly while attacking an enemy.
At the options menu, select Cheats and enter "XXEVPIKS"
Vexx can do a slower, more powerful version of his 3-hit combo by pressing attack at a slower pace, and holding it on the last blow. Vexx does a moderately powerful uppercut that refills more of his special meter. Use R to use the super move at the right time.
At the options menu, select Cheats and enter "XXEVTOOFYTFIF"