Hi Five Ghost is a small, pale ghost. He is semi-transparent as you can see through him, but not completely through. He has basic features, eyes, and a mouth, and also has one hand sticking out of his head. It was revealed in Go Viral that Hi Five Ghost has four extra arms, or it is possible that he can spontaneously generate any number of arms that he wants. In Gut Model, it is seen he can transform into a shield.
He and Muscle Man seem to be best friends, since they are always assigned jobs together. When Muscle Man is in a frame, it is to be assumed that "Fives" is along with him. The two are nearly inseparable (As Hi Fives always quits whenever Muscle Man gets fired), just like Mordecai and Rigby. When he appears, he is always with Hi Five Ghost. Similar to how Benson never gets mad at Mordecai alone, HFG never makes fun of Mordecai or Rigby by himself (he is always with Muscle Man when this happens).
- Hi Five (or High Five)
- Hi Fives (or High Fives)
- Undead - Even though it is unknown if he was born alive, Hi Five is shown to be a ghost and lives and interacts with others, even though he's a ghost.
- Trumpet Player - In This Is My Jam, it is shown that Hi Five Ghost can play the trumpet, even though Muscle Man blows into the mouth piece.
- Loud Laughs - Even though Hi Five is usually silent, he has a very loud laugh, which can be proven in The Night Owl.
- Floatation- Hi Five Ghost can float instead of walk and never gets tired of doing it.
- Goes Through Everything - As revealed by his brother, they can go through walls and objects.
- Ability to Form a Shield - In Gut Model, it was revealed that Hi Five Ghost can turn into a shield.
- Pranks - He is a master pranker alongside Muscle Man.
- Hot Wiring - He can also hot-wire a car to go very fast, as seen in the episode My Mom.
- Despite his name, Hi Five Ghost is shown to only have four fingers. Though, his four other hands have five fingers. His name may reference the 'high-five' position his main hand is in.
- It is possible that he was turned into a ghost like Mordecai and Rigby, and never got turned back.
- Most of the time he is never heard because when he speaks Muscle Man usually talks over him.
- He and Muscle Man can be seen with the crowd of people in the Pilot episode watching Mordecai and Rigby playing Rock, Paper, Scissors.
- When Muscle Man is fired in Don, Hi Five Ghost goes with Muscle Man, even though Hi Five is not fired.
- Hi Five only has a little dialogue in the series despite the fact that he is a main character.
- It is unsure if he's as arrogant as Muscle Man, although he does seem to agree with the insults Muscle Man calls out to Mordecai and Rigby.
- HFG might also have the ability to turn people into ghosts.
- Hi Five Ghost's nickname is Fives when Muscle Man and him flee after they think that a "bucket with wheels" stole Rigby's voice in the episode Rigby's Body.
- Hi Five Ghost wears a four fingered spiked brass knuckle when Rigby's consciousness was emptied into the garbage truck.
- In Rigby's Body, we finally hear him speak when he says to Rigby "What are you?". In the episode, Just Set Up The Chairs, he can be heard saying "Yes! Uh!" with Muscle Man, though this is barely heard.
- Hi Five Ghost is almost always smiling.
- Hi Five Ghost first frowns when he carries Rigby down from the roof in Death Punchies.
- Hi Five Ghost is a ghost, but it is not explained who he is the deceased form of.
- In the episode My Mom, Hi Five Ghost actually has three arms instead of one located on top of his head. His other two arms are on the sides.
- Hi Five's hand on his hand looks like a fork, while his other two hands that come out of the side of him have 5 fingers and actually look like human-hands.
- In Just Set Up The Chairs, it is the first time Hi Five smiles without his mouth open. Second is Don.
- Even though it is shown Fives has four other hands, he often does more stuff with his top hand on his head.
- It is shown that Muscle Man's Uncle John taught Hi Five how to fix the engine in the golf-cart to make it go speeding fast. Though, Muscle Man probably was lying, because Fives high-fived him afterwards. Though it's possible that he was saying it was cool that his Uncle John taught him.
- It's possible that Hi Five is also hurt when someone says that Muscle Man doesn't say his jokes right.
- Hi Five Ghost is a great bowler as proven in My Mom.
- Hi Five Ghost holds up the rock sign many times in My Mom.
- Hi Five Ghost likes to annoy Benson, along with Muscle Man. This is proven in Don.
- Hi Five Ghost is a fan of Fist Pump. This is proven in Caffeinated Concert Tickets.
- In Death Punchies, it's unknown why Rigby punches him because he is not shown to have beaten Rigby at Punchies. Also, he is shown to be hit, but he is not shown with Muscle Man smashed into the building, which may mean that he is weightless and had floated into the air like a balloon.
- When Hi Five shouts "OOOOOHHHH!" with Muscle Man and the Taco'Worker, he is not heard.
- Hi Five Ghost has many nicknames, including Hi Five, Hi Fives, Fives, HFG, and Five.
- In the episode Benson Be Gone, Hi Five turns to normal because didn't do what Susan said, and then drinks a whole can of soda.
- This Is My Jam marks the biggest expression on Hi Five's face and also marks the only time he frowns with his mouth open.
- Hi Five Ghost is voiced by J.G. Quintel, but was voiced by Jeff Bennett in early episodes.
- Hi Five Ghost's facial expressions resemble those of the faces of Comedy and Tragedy that are in plays and theaters. Both of these expressions are used in Don.
- In Jinx, he was unaffected by the Jinx monster's scratch probably due to intangibility, though he didn't use it when punched by Muscle Man.
- In See You There, Low Five, his brother says that ghosts can't be hurt but he is punched multiple times by MM in Jinx and hurt and pummeled by the Hammer in "Rage Against the TV."
- Hi Five Ghost sounds elderly when he says "Uh-huh" in Rage Against the TV.
- The credits credited J.G. Quintel, Mordecai's voice actor, for voicing him in "Just Set Up The Chairs" and "Rigby's Body," even though Jeff Bennett voiced him. Though, Quintel voices him in season two and onward.
- Interestingly, Mordecai and Hi Five are frozen next to each other in The Night Owl.
- With the exception of Hi Five Ghost, all of the main characters have been antagonists at least once (although the real Pops isn't an antagonist, Mordecai's memory of nude Pops is).
- Hi Five Ghost resembles his father and brother.
- In the episode Go Viral, it is revealed that Hi Five Ghost has five arms: the one on his head and another four which he keeps hidden.
- He thinks the internet sensation Wedgie Ninja is funny.
- Hi Five Ghost has the second most family members actually seen in the series (Being his dad and brother; both in "See You There"). Benson has the most family members while Rigby, Muscle Man, and Pops have one (Pops having his father, Mr. Maellard, Rigby having his brother, Don, Muscle Man having his brother John, and Benson having his mom, dad, and sister) and Mordecai and Skips have none.
- His smile and frowny face are similar to Poes from the Legend of Zelda, mainly the ones from Ocarina of Time.
- The bottom part of his body and his shape could be a resemblance to the ghosts from Pac-Man.
- He began to say full sentences in "Muscle Woman" and has been ever since.
- Hi Five Ghost spoke more than he ever has in "Gut Model".
- He can also change color; sometimes he's green and sometimes he's white.
- In season 3, him and Muscle Man have become nicer and friendlier to Mordecai and Rigby.
- In Trucker Hall of Fame, it revealed that he dosen't take people's deaths well since he is seen crying outside the funeral.