X is an algebralian, variable and the co-host of BFB. They were the host after Donut resigned until Four's return. X is a drawing of the letter X with a yellow body and lighter yellow limbs. Similar to Four, they are purposefully drawn simplistically, with different assets and four fingers. X plays a role as Four's assistant.

He sets up some of the challenges, as seen in "Getting Teardrop to Talk".