Four

Four is the main host of Season 4, Battle for BFDI. Four has very surrealistic mannerisms, like being able to deform characters, revive them, screech in order to stun characters, eliminate contestants by sucking them into his head and having the ability to shoot laser beams. Four's first appearance in BFDI is Getting Teardrop to Talk, where they lead a game to win "a BFDI" (in which it means the winners will get another battle for Dream Island). Four appeared alongside X, another abstract being representing a real-life number, letter or variable.

Personality
Although Four seems calm most of the time, he appears angry in BFB 2 and BFB 3 for a few times. Cary Huang has suggested that he and X are some sort of extra-terrestrial being. Four was nice in XFOHV and didn't screech then.

Coverage
Four's first appearance was in a 2008 animation by Jacknjellify called X Finds Out His Value along with X, where he helps X figure out his value by factoring out an equation.

Nine years later, Four and X appear in BFB as the hosts. Unlike his original appearance, he acts extremely odd and screeches at others who try to talk to him, making them faint, become dizzy, or even die (in the case of Pillow). The only two characters who can actually communicate with him properly are Dora and Roboty for some reason, who each also only talk in a strange manner. He can understand X, as seen in XFOHV and BFB 3. His color was changed from Dark Blue to light blue.

Deaths

 * Why Would You Do This on a Swingset: May have died when Balloony crushed his earth with his finger (Debatable).

Kills
Total kills: 5

Powers and abilites

 * Screechy: Stuns any contestant who tries to talk to Four.
 * Energy Beam: Electrocutes the contestant who is touched, and makes him lose health.
 * Recovery center: Four replaces the Recovery Centers from previous seasons, with his hand.
 * Drawing transformation: Turns any contestant into a badly-drawn version of themselves, killing them.
 * Elimination: Four replaces the TLC and LOL from previous seasons, by sucking eliminated contestants into him. (Balloony says the eliminated contestants are in Eternal Algebra Class.)

Trivia

 * He appears to have four fingers on each hand, however, when he is grabbing Black Hole before the intro, he has five.
 * He appeared in the HTwins.net game Tidepool, as a level 23 creature in the "Classic" character set.
 * Cary described Four as a "weird alien creature who doesn't know how to communicate" in his reaction video. If he actually is an alien, this could explain his strange powers, general behavioral quirks, and different eye and limb assets, as well as his screeching.
 * He explains challenges in a way where the problem is shown (performed by X, sometimes himself) and he instructs the objects to the task as a challenge.
 * Four seems to be omnipotent. However, being omnipotent doesn't grant him the ability to give good solutions to the problems which he is faced with all of the time.
 * He has the ability to recover and kill contestants, replacing the Recovery Centers for this season.
 * He can also transport eliminated contestants to an unknown place (referred to as "eternal algebra class" by Balloony) by sucking them into himself, replacing the Tiny Loser Chamber and Locker of Losers
 * Four might represent the show's fourth season, although there's no clue of what would happen to him in season 5.
 * Four accidentally calls the team A Better Name Than That "Another Name Than That" in BFB 2, a running gag in the BFDI series whenever Golf Ball can't think up a team name.
 * Four and X have terribly animated mouths sometimes.
 * Four was originally a darker shade of blue.
 * When he and X sometimes talk, they are just different assets used over and over.
 * Four can shoot energy beams from his hands.
 * Four starts the intro in every episode by raising his right arm in a fist.
 * Four is able to talk with his eyes, as shown in Why Would You Do This on a Swingset.
 * Four might also use "it/its/itself" pronouns since Pie referred to him as an "it" in Getting Teardrop to Talk. Those pronouns could, however, be placeholder pronouns, since Four's gender wasn't known by the contestants at the time.
 * According to Balloony, Inside his body is a prison of eliminated contestant with Eternal Algebra Class.