The Secret Society is a clandestine group of wizards based out of Wizard City consisting of Forest Wizard, Laser Wizard and the toad host of Bufo, though the Ice King frequently crashes their meetings. They are dedicated to achieving the "highest initiations of the secret schools" through dangerous rituals, which carry potentially destructive consequences for them or others caught in their path.Their official sign is a "W" formed with a hand by holding two middle fingers together with the fingers opposite them spread out, and the thumb folded into the palm. This is usually done while reciting the society's official oath:
In shadow, we find the light,
Safely sealed in darkest night.
So make sure y'all keep it tight.
Wizards only, fools!
The society first appears in "Reign of Gunters" when Ice King stumbles upon their meeting in a magic shop while looking for a replacement for his Demonic Wishing Eye that has been stolen by Gunter. He comes in just as Bufo is finishing his tale about how he took advice to "beef in the eye of Glob and stuff," which impresses Laser Wizard and worries Forest Wizard, who says he would not have done that. After overhearing their oath, Ice King asks what they're keeping tight, which prompts the society to try to kill him, despite Ice King's denials of "hearing nothing about no secret wizarding club I want to be a part of." Later, a badly disheveled Ice King appears in the Candy Kingdom, indicating he escaped the society, and after stopping Gunter, starts to tell the others about the showdown before remembering and reciting part of the society's oath, showing he considers himself part of the society.
In "Wizards Only, Fools," Finn, Jake, and Princess Bubblegum are fleeing the Wizard Police for entering Wizard City as non-magic beings and attempting to buy potions from Ron James ' magic shop when they encounter Abracadaniel, who has apparently been hired to sweep up for the society. Unbeknownst to Abracadaniel, the society is planning to "extract his forehead" in a sacrifice ritual, but they are interrupted by the Wizard Police barging in and attempting to arrest everyone for harboring non-magic-users. The society uses a chant to gain passages from the "ghosts of the warp plane," which causes them to vanish, leaving their clothes behind. During this ritual, a transparent Ice King is seen watching them from a bookcase, either from an invisibility spell or a hologram projection.
In "Betty," the society is back in Wizard City and as the episode begins, offers up the staff of Stranson Doughblow in the final stage of an elaborate ritual to summon the creature Bella Noche and gain access to the system of antediluvian magics, which they consider "the tightest of all wiz-biz." Once again, Ice King has crashed the meeting, but before they can deal with him, the Wizard Police and Grand Master Wizard interrupt and reveal Bella Noche is an anti-magic creature, just as it emerges and steals all their magics, turning Ice King back into his human form of Simon Petrikov. Forest Wizard and Laser Wizard are seen with their powers again at the end of the episode after Betty Grof defeats Bella Noche.
- The society's oath is similar to the Green Lantern oath from DC Comics; however, according to Jesse Moynihan, it is not a parody.
- The "Wizards Only, Fools" hand sign is similar to the "Live Long and Prosper" gesture by Mr. Spock from Star Trek.
- The society itself is similar to the Trio from Buffy the Vampire Slayer, a group of minor characters from previous episodes who banded together to make dangerous magical and scientific experiments to increase their own power.
- A "Wizards Only, Fools!" medallion with Ice King making the society's gesture was the prize for completing the Adventure Time scavenger hunt at the 2013 San Diego Comic-Con.
- In "Thanks for the Crabapples, Giuseppe," Ice King starts his own "less jerky" secret society with Abracadaniel, Ron James and other misfit wizards. It is shown that there are a number of other "secret" wizard societies in Wizard City, one of which's members openly do a "secret wizard handshake" and brag about the "secret thing tonight" mostly as an excuse to openly disinclude other wizards such as Abracadaniel.