Blacephalon is a colorful, humanoid Ultra Beast. Its slender torso and wide hips are yellow with alternating blue and pink stripes. There is a white sphere in the middle of its body and another on its back in place of a tail. It has thin arms with white frills on its wrists and teardrop-shaped hands. The right arm is pink, while the left is blue. Each arm has a spherical bulge near the shoulder. Its legs are shaped like white high-heeled boots with curled toes. Each foot has a sphere on it: blue on the left and pink on the right. Around its neck is a white frill with a hole in the center.
Blacephalon's head is a white ball with a multitude of pink and blue dots, which are a collection of tiny sparks. On either side of the ball are stars that are blue on the outside, pink on the inside, and have yellow dot-like eyes on the center. The head is not attached to the body and can be removed for use as a weapon. As seen in Pokémon Refresh, the color of the sparks and the color and shape of the stars change with Blacephalon's mood. It is known to trick its targets through the silly way it walks before blowing its head up without warning, shocking them in the process; it then steals their vitality to use as energy. As seen in the anime, this Ultra Beast can freely move its head around easily and regenerate it after blowing it up.
Blacephalon debuted in Twirling with a Bang!. Ash and his classmates first encountered it performing during a fireworks show. The next day, they learned that it was an Ultra Beast and set out as the Ultra Guardians to capture it. However, they also ran into a Xurkitree while trying to find it, and soon, the two Ultra Beasts ended up in a performance showdown, each trying to outperform the other with their moves. Thanks to a distraction from the Ultra Guardians, they were able to distract, weaken, and subsequently capture the two Ultra Beasts at the same time, allowing them to be returned home wherever they come from. It reappeared in a flashback in Securing the Future!.