Gumball Guardian

The Gumball Guardians (also known as Guardians of the Royal Promise) make their first appearances in the episode "Slumber Party Panic." They are first seen on opposite sides of Princess Bubblegum's Castle blowing bubbles. The Guardians will freeze time and appear to anyone who breaks a royal promise and destroy them. Usually they hold a (literal) trial by fire to the promise-breaker. However, in "Slumber Party Panic," Princess Bubblegum manages to stop the trial by fire because of her friendship with Finn, so instead they ask Finn a math question: originally long and very complex (and involving an approximation of pi), but one of the Guardians changes his mind and instead gives the question of what is "two plus two." Finn is terrible at math, yet correctly guesses "four." The guardians' heads then blow up, reversing time to just before they came to grab Finn and the princess. They then go back to their places on the sides of the Candy Palace and begin blowing bubbles again.

They also appear in "Ricardio the Heart Guy" when Finn and Jake are spying on Ricardio in the Candy Kingdom, though they remain dormant in this episode. In "Mortal Recoil," Princess Bubblegum (while possessed by The Lich) attacked one of the guardians. It said, "Evil presence detected! Must defend!" while grabbing the hands of the princess. It was defeated, however, and can later be seen on the ground with a broken head. In "The Lich," one of the guardians detects the Lich disguised as Billy, where it proceeds to attack. They appear almost every episode that the entire Candy Kingdom is shown, most of the time sitting on the left and right walls of the kingdom, blowing bubbles.

Appearance
The Gumball Guardians are two giant gumball machine men who wear ice cream cones on their heads as hats. Their skin may or may not be pink, as it is possible they could simply be wearing colorful shirts.

Quotes
"Finn the human! You have broken a royal promise, for which the penalty is trial by fire. Because you care for the promise-breaker, we will give him a less hot trial. You must now answer math questions."

"Oh wait, wait. I thought of a better one. Yes! Two plus Two! Solve it or die."

"Evil presence detected! Must defend!"

Major appearances

 * "Slumber Party Panic"
 * "Mortal Recoil"
 * "Reign of Gunters"

Minor appearances

 * "From Bad to Worse"
 * "Apple Thief"
 * "Fionna and Cake"
 * "Too Young"
 * "Go With Me"
 * "Susan Strong"
 * "What Have You Done?"
 * "The Duke"
 * "Trouble in Lumpy Space"
 * "Ricardio the Heart Guy"
 * "The Lich (episode)

Trivia

 * In Princess Bubblegum's lab, there is a dummy Guardian of the Royal Promise. It is seen after the real Guardians leave her and Finn.
 * In "Ricardio the Heart Guy," when Finn decides to spy on Ricardio, one of the Royal Guardians appears to be missing his cone hat.
 * In "Ricardio The Heart Guy," there are two smaller Royal Guardians in the throne room where Ricardio holds Princess Bubblegum hostage. They are seen wearing royal cloaks and blowing horns.
 * Their voice actors are Jeremy Shada and John DiMaggio, who do the voices of Finn and Jake.
 * In "Mortal Recoil," the way the Guardian speaks resembles the dialect used by the Daleks, from the sci-fi TV series Doctor Who.
 * A Royal Guardian's head is seen in Jaybird's lair in the episode "Apple Thief."
 * The Guardians also seem to resemble Benson from Regular Show. Or Tom Servo from sci-fi comedy TV series Mystery Science Theater 3000.
 * Strangely, they do not become or fight the Candy Zombies.
 * Whenever they sense danger to the candy kingdom they say "Evil presence detected, must defend."
 * In "Mortal Recoil," one of the Guardians has his glass bowl head broken without consequence, but in "Reign of Gunters," when Gunter threatens to do the same, the Gumball Guardian reacts as if such an act would be fatal.