X

X is the secondary host of Battle for BFDI. X's first appearance in BFDI is Getting Teardrop to Talk where X and Four lead a game to win "a BFDI" (in which it means the winners will get another battle for Dream Island). X appeared alongside Four, another abstract being representing a real life number or variable.

X played a major role in the challenge in Getting Teardrop to Talk. The contestants had to return a basket back to X, who was standing on a tall platform, in order to avoid elimination.

X's first appearance was in a 2008 animation X Finds Out His Value along with Four, nine years before first appearing in the BFDI series. This also shows that X doesn't refer to the English letter, but the algebraic variable.

Trivia

 * In the animation X Finds Out His Value, the value of X turned out to be 7.
 * X appears in the HTwins.net game Tidepool, as a level 24 creature.