Viewing the gamedata file for Kingsley's Adventure in Notepad reveals some unused dialogue, including some for a boss fight with a character named Waldo that does not exist.
"Defeat Reggie and we will be free!"
This dialogue was undoubtedly intended for the prisoners at the end of Reggie's Castle Ruins, but there is no way to talk to them.
"Waldo! What happened to you, why are you here?"
"Waldo. It's me, Kingsley. We are friends, remember?"
"No. Waldo has no friends, I obey Bad Custard. Prepare to die!"
This all appears to be dialogue from before the fight with the excised Waldo boss.
"Ouch! What was that? Where the...Kingsley!"
"Hello Waldo, I hope I didn't hurt you too bad..."
"Where are we? Why where we fighting?"
"You've been under the influence of evil Bad Custard, he's been using you."
"Bad Custard! Now I remember."
"I'm hurt bad Kingsley, you'll have to do it alone."
The post-fight dialogue suggests that the spell on Waldo was broken. There is no character named Waldo in the game and it is unclear where this boss fight was intended to take place, though the dialogue suggests it would have come right before fighting Bad Custard, the final boss.
A folder on the game's disk contains all the boss themes and a few other songs in RAW format. Three of them are unused: "SVEN", "CRAB", and "SYLVESTA". There are no characters with these names anywhere in the game. It should be noted that the gamedata file lists the name "Sylvester" right along with "Waldo" and all the unused dialogue. This heavily suggests that Sylvester and Waldo are one and the same, considering that most of the game's bosses are an animal with one name that is transformed by Bad Custard's magic into an animal with another name. Example: William the Frog is transformed into Rex the Crocodile. Defeating him changes him back to normal.
Source: Flying Omelette