There are six hidden characters that can be unlocked to be used in challenge mode and against another player. What you need to do is highlight a certain character and press the C/3 button three times within a second.It isn't as bad as you think though, since you can choose which second in the countdown to press the C/3 button three times.20 - Judgment19 - Sun17 - Star15 - Devil13 - Death11 - Justice8 - Strength7 - Chariot6 - Lovers5 - Hierophant4 - Emperor3 - Empress2 - High Priestess1 - Magician0 - FoolIf done correctly you will see the hidden characters appear about a second later. The characters unlocked this way are: Moon, Hanged Man, Hermit, Temperance, Tower, and Fortune. You will also gain 10 seconds to the countdown, which can go up to the max of 20.
Hit B on any character to get their alternate colors.
Highlight Strength and while holding the C button, press either the A button or the B button to play as Father Strentgh. The button you pressed determines his outfit.