Ice Magic

Ice Powers are the abilities possessed by the Ice King, and similarly the Ice Queen in the gender-swapped version. Ice King claims to have stolen them, assumably from another wizard, and sealed them in his crown. In the episode "Holly Jolly Secrets Part II" it is revealed that he found the crown in Scandinavia as a collector, unaware that the crown would grant him ice powers or drive him into insanity. Consequently, he loses his Ice Powers if his crown is removed or lost. The main application of Ice King's powers are the large icy lightning bolts he shoots at his opponents. He can also manipulate the water in the air to create shields, and can even create torrents of icy weather at will. As seen in "The Eyes," the Ice King is also able to manipulate any ice in the area telekinetically.

Strangely, while the Ice King is rather incompetent and weak on his own, the ice he controls is extremely sturdy and strong, completely incapacitating anyone frozen within preventing any movement. It's only weakness is the common fragility of ice which can shatter but it still can show strength in such: after freezing Princess Bubblegum (who had mutated into a giant monster courtesy of The Lich) in "Mortal Recoil," the ice prison did shatter but it was strong and stable enough to shatter Bubblegum's entire body in the process. The freezing completely stopping all life and motion of the target can be both a blessing and a curse: while it does allow for Ice King to easily stop opponents, it becomes a burden when he must carry his target while they're still incapacitated, sometimes relying on a cart (in the Ice Kingdom) to bring someone he had frozen to imprison in his castle.

Even though the Ice King does possess a weakness towards heat and fire, he can withstand it for a period of time if need be. When trying to protect Finn and Jake from Scorcher in "Hitman." he created a strong ice dome that withstood the fire elemental's power for a longer period of time than one would typically consider the interaction between ice and fire.

Another common use of his Ice Powers is the Ice King's ability to fly. This is done through the animation of his beard, which act as wings. In the episode "Loyalty to the King," it is revealed that if his beard is shaved off, he loses his power to fly.

Fridjitzu
Fridjitzu is an extension of the Ice King's powers. It is a play on the words 'Frigid' and 'Ninjitsu.' Where as his main attacks are generally broad and unfocused, the techniques held in the Ice Ninja manual Ninjas of the Ice: The Art of Fridjitzu enable the Ice King to use more refined attacks, and even create weapons out of Ice. He generally keeps this range of his abilities a secret and rarely uses it in battle. Finn and Jake learned a few techniques in Fridjitzu when they found the manual in Ice King's home, but forgot what they had learned shortly afterwards.

Trivia

 * Ice King also has an ability called Wizard Eyes that causes him to see bizarre and disturbing things that don't make sense. It is revealed in "Holly Jolly Secrets Part II" that he can't control whether or not he sees the visions even without the crown.
 * The Ice King also possesses a Demonic Wishing Eye and Ghost Pouch, although it is unknown if these things are connected to his Ice Powers or another form of wizardry.
 * The Demonic Wishing Eye may be an allusion to the "Evil Eye," an Italian superstition popularized by the "Devil Horns" hand gesture, made famous by Heavy Metal vocalist Ronnie James Dio.
 * It is shown that Ice King can make large objects with his ice powers, as in "Mortal Folly," where he makes a large ice dome in an attempt to trap Finn and Jake so he could get their permission to marry Princess Bubblegum.
 * The crown he wears could make a person insane and a regular man's body color change to blue and the person's body temperature lower.
 * The Ice King can see all things in the spirit realm probably a side effect of the crown as seen in "Beyond this Earthly Realm."
 * It is revealed that the Ice King can make living things out of snow as seen in the episodes, "Holly Jolly Secrets Part II" and "When Wedding Bells Thaw"