Gumball Guardian

The Gumball Guardians (also known as Guardians of the Royal Promise) make their very 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!"

"Lich alert! Lich alert!"

"MUST DEFEND Candy Kingd... wraghhhhh"

"Peanut Butler, eh, Peppermint Butler, cease these dark magic activity."

Abilities
Gumball Guardians have a wide range of offensive abilities, including breathing fire, using runic lasers that cause large explosions, and hand to hand combat. They are able to detect evil presences in the Candy Kingdom, even something as small as an evil hat. They are also quite skilled in advanced math.

Major/Moving appearances

 * "Slumber Party Panic"
 * "Mortal Recoil"
 * "Reign of Gunters"
 * "The Lich"
 * "Little Dude"
 * "The Suitor"

Minor/Non-Moving appearances

 * "From Bad to Worse"
 * "Fionna and Cake"(Ice King's fan fic)
 * "Too Young"
 * "Go With Me"
 * "Susan Strong"
 * "What Have You Done?"
 * "The Duke"
 * "Trouble in Lumpy Space"
 * "Ricardio the Heart Guy"
 * "Bad Little Boy"(Ice King's fan fic)
 * "Five Short Graybles"
 * "Five More Short Graybles"

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."
 * 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.
 * They closely resemble in appearance Benson from Regular Show.
 * They are set off by "evil presence," which they can detect. However, neither Ice King nor Marceline triggers them.
 * Though this could be because Marceline isn't intentionally evil and The Ice King is only a minor threat in comparison to The Lich.