Four

Four is the main host of Battle for BFDI. Four and his co-host X first appeared in the pre-BFDI video X Finds Out His Value.

Four has very surrealistic mannerisms, including being able to deform characters, reviving them, screeching in order to stun characters, eliminating contestants by sucking them into his body (sending them to Eternal Algebra Class), and having the ability to shoot laser beams from his hands.

Four's first appearance in BFDI is Getting Teardrop to Talk, where they lead a game to win "a BFDI" (in which the winners will possibly 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 to be calm most of the time, he appears angry in BFB 2 and Why Would You Do This on a Swingset for a few times. Cary Huang has suggested that he and X are some sort of extra-terrestrial beings. Four was nice in XFOHV and didn't screech then.

Powers and abilities

 * Screechy: Stuns any contestant who tries to talk to Four. It can also generate hearts when Four is excited, which can fling a contestant.4screaming.PNG
 * Energy Beam: Electrocutes the contestant who is touched, and makes them lose health.
 * Recovery center: Four replaces the Recovery Centers from previous seasons with their hand.
 * Drawing deformation: Turns any contestant into a deformed version of themselves, killing them.
 * Elimination: Four replaces the Tiny Loser Chamber and Locker of Losers from previous seasons, by sucking eliminated contestants into them or "eating" them. (Balloony says the eliminated contestants are sent to Eternal Algebra Class.)

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 Battle for BFDI as the hosts. Unlike their original appearance, Four 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.

Kills
Total kills: 2-7

People screeched
Total screeches: 11

Trivia

 * They are depicted with four fingers frequently, but sometimes they are depicted with five, as seen during the intro of Getting Teardrop to Talk where they shrink Black Hole and before blasting energy beams at Gelatin in Why Would You Do This on a Swingset.
 * They 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 they actually are an alien, this could explain their strange powers, general behavioral quirks, and different eye and limb assets, as well as their screeching.
 * They explain challenges in a way where the problem is shown (performed by X, sometimes themselves) and they instruct the objects to the task as a challenge.
 * Four seems to be omnipotent. However, being omnipotent doesn't grant them the ability to give good solutions to the problems which they are faced with all of the time.
 * They have the ability to recover and kill contestants, replacing the Recovery Centers for this season.
 * They can also transport eliminated contestants to an unknown place (referred to as "Eternal algebra class" by Balloony) by sucking them into themselves, 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 them in season 5 (if there is one).
 * Four accidentally calls the team A Better Name Than That "Another Name Than That" in BFB 2 and BFB 4, a running gag in the BFDI series whenever Golf Ball can't think of a team name.
 * Four and X have terribly animated mouths sometimes.
 * Four was originally a darker shade of blue.
 * When they and X sometimes talk, they are just different assets used over and over.
 * Four can shoot energy beams from their hands.
 * Four starts the intro in every episode by raising their right arm in a fist.
 * However, this isn't the case in BFB 4, when the intro plays after Bell says "Are you kidding me!" Before that, Snowball goes into that pose.
 * Four is able to talk with their eyes, as shown in Why Would You Do This on a Swingset.
 * Four's gender is not known by the contestants at the time. None of the contestants have referred to Four by any gendered pronouns, and Four was not included on Satomi's gender confirmation chart. They might use "it/its/itself" pronouns since Pie referred to them as an "it" in Getting Teardrop to Talk. Cary Huang has referred to Four as a male, but since Satomi said the episodes are canon, not what the creators say, it's possible that this isn't true.
 * According to Balloony, inside their body is a prison containing eliminated contestants. This prison is called "Eternal Algebra Class".
 * Their screeching may have become a meme as there were over 10 videos on a YouTube of them screeching.