Finn

Finn Mertens (also called Finn the Human, Pen in the original short, and identified as P-G-8-7 Mertens) is one of the main characters in Adventure Time.

Physical
Despite his age and appearance, Finn seems to be quite strong and athletic; he can be seen wrestling full-grown Marauders, the large grass ogre Donny, and a general variety of monsters and creatures several times his size. Finn is also capable of lifting up Princess Bubblegum, as shown in "Mortal Recoil" when he picks her up and puts her in her bed, and capable of lifting up Marceline as seen in "Daddy's Little Monster." In addition, he is able to pick up a tree and hit Barb, a giant spider, in "Web Weirdos." In "Another Way," Finn is able to run long distances while carrying a giant cyclops' eye. Lastly, in "Dad's Dungeon," when Finn stabs the Evil Monster in the eye, he is able to lift it up slightly off the ground and flip it into the pit. Being the size it is, the giant Evil Monster should have weighed at least several tons, thus showing Finn's strength. Finn is also agile as he can jump very high and even make his arms and legs bend in inhuman ways, as during the Science Dance and when he uses "spaghetti limbs" (waving his arms and legs, which Jake can also do). In "The New Frontier," it is shown that Finn can make fire only with his hands.

Finn is very tolerant of pain as in "No One Can Hear You" he merely says "whatever," when the Stag breaks his legs. Finn can also endure high temperatures, as seen in "Jake Suit" as he allows Jake to dip his head in lava, and also in "Rattleballs," when he sits in a mini-barbecue. This may be because he is already accustomed to heat from his relationship with Flame Princess. Also, in "The Lich," he is able to break the Enchiridion on his knee without any sign of pain, demonstrating considerable strength and resilience. He even tries to teach Jake how to tolerate pain in "Jake Suit," when he says, "just pretend like every bruise is a hickey from the universe." Finn seems to have impeccable balance, as he is able to balance himself on two wheels in his wheelchair in the episode "No One Can Hear You." However, he refers to it as "skills." Finn is known to have deuteranopia, a form of heredity dichromatism that makes it difficult to distinguish green hues from red, as shown in "Red Starved." As this is a sex-linked genetic condition inherited on the X chromosome, Finn must have inherited the condition from his mother.

Finn has obtained immunity to electricity thanks to magic spring water in "Flute Spell"

This ability seems to have stuck with him as we see him display the weakness of electricity in "Preboot" against a giant electric eel and again in "The Light Cloud' against the Great Guardian.

Mental
Finn has the ability to mentally fight psychic abilities. The first time he shows this during the Lich's attempt to control his mind. The second time was against Goliad, as he was constantly able to manipulate his own thoughts in order to avoid revealing the plan to defeat her, allowing Princess Bubblegum to create Stormo.

Finn can focus for a very long time as shown in "Still" when he spends hours telepathically summoning an Astral Beast. As demonstrated in "The Creeps," Finn can lock unwanted memories in "The Vault," which is later seen in "King Worm." However, this is considered a normal human ability that occurs where certain memories are removed from consciousness if it is too painful or traumatic for them to recall. Finn also has the ability to read and write, and he can also do simple math.

Fighting Style
Finn is proficient in several forms of combat, including hand-to-hand, magic, and swordsmanship. When using hand-to-hand combat, he is an aggressive fighter, combining some forms of martial arts or his amazing swordsmanship skills. Finn prefers overpowering his opponents, but he is also quick enough to understand an opponent's weakness or using his environment to win a fight. He also received training from the old gumball robot Rattleballs which dramatically improved his sword skills and his reflexes to greater levels.

Creativity
Besides combat, Finn displays many other impressive abilities in handicrafts. He has some origami skills, as shown in "Ricardio the Heart Guy," in which he makes Princess Bubblegum a paper crane, as well as in "Marceline's Closet," in which he makes a paper airplane. In addition to that Finn can also draw as seen in "The Thin Yellow Line" which he states that he isn't very good at it, as well as in "Mysterious Island" where he draws BMO and Susan. He is shown to be able to construct a sculpture of the Candy Kingdom from his saliva for Princess Bubblegum in "The Real You." Finn is also somewhat gifted at constructing simple machines, such as the catapult in "The Witch's Garden."

Musical
Finn enjoys singing; after swallowing a tiny computer, he gains the ability to Auto-tune his voice on command, although he can sing without it as well. Apparently, Finn can also play the flute, as seen in "Prisoners of Love," where he plays a short lick before javelin-throwing it at Ice King. Unfortunately, the flute falls apart before it could hit him. Because of this, Finn is not seen playing the flute until "The Lich" as Farmworld Finn and near the climax of "Finn the Human" when he shoves it into Tromo's nose. He is also very good at beatboxing as seen in "It Came from the Nightosphere" and "What Was Missing."

In "Gut Grinder," Finn tries to play Jake's viola, but Jake says he stinks. Jake even imitates his footprints and said: "I'm Finn the Human, and I stink at viola." However, during "Death in Bloom," Finn panicked over what instrument to pick, supposedly because he could not play any of them, and settles for sleigh bells. In the episode "Go With Me," Finn is seen playing the lute. In "Daddy's Little Monster," he is seen playing the tambourine.

Miscellaneous
Finn is very good at playing a video game called Adventure Master, which he and Jake play on BMO from time to time. Finn can also spit very long distances, as he demonstrates in "Evicted!," when he spits on Marceline, "My Two Favorite People," when he spits on Tiffany's face, and in "Web Weirdos," when he spits on birds flying overhead, while suspended upside down on a giant spider web. In "Dungeon," one of the trials that Jake says Finn would have breezed through is a spitting competition against a goblin-like creature. In "Burning Low," Finn is shown to be able to spit water incredibly high into the air. In "Who Would Win," Finn showers Jake with an abnormal amount of saliva through spitting. He also handles his sword with his right hand, suggesting he may be ambidextrous, able to use both hands with equal skill. This is also seen in "Frost & Fire," where Finn writes with his left and right hands and, occasionally, both at the same time. Finn is able to cook, although he leaves this task mostly to Jake. However, in "In Your Footsteps," it mentions and shows him making Finn Cakes.

Temporary/Magical
Finn and Jake gain magical abilities in the episode "Wizard," but they never use those abilities in any other episode. Pendleton Ward later revealed on his Spring that all of the magic that Finn and Jake gained in that episode was contained in their robes, which were destroyed. Likewise, in "The Chamber of Frozen Blades," Finn and Jake gain ice-ninja skills, but it is unlikely they will use them again because, according to Adam Muto, "They didn't have enough time to commit the incantations and hand positions to memory." Finn seems to speak Latin (as evident in "Morituri Te Salutamus,") although this may be caused by the magical powers of Fight King's arena. In "Daddy's Little Monster," for the first time, he becomes an antagonist by wearing the Nightosphere amulet, although it is only temporary. In "The Tower" Finn gains a new mental arm with the ability to interact with the physical world. His emotions seem to cause this, along with the ability of telekinesis. Since it was linked with his emotions, it exploded into a huge arm of spikes when he confronted his "dad," and disappeared when Finn's animosity abated.