Skulls are objects present throughout ULTRAKILL that act like keys.
Skulls come in two colors, red and blue, and both colors are identical in function, although a blue Skull cannot activate a red pedestal, and vice-versa. Skulls are often found on pedestals, and are picked up by punching them. When placed upon the matching color of pedestal, it activates whatever the pedestal was connected to, usually a door. They are first formally introduced in [ 1-1 /// HEART OF THE SUNRISE ], although the blue Skull appears earlier as part of a secret in [ 0-2 /// THE MEATGRINDER ].
- In [ 1-4 /// CLAIR DE LUNE ] a blue Skull can be placed upon the headless, praying skeleton at the altar, which does nothing but prompt the text "Nothing happens, but you feel a strange satisfaction. You decide to name it Hank."
- [ 1-4 /// CLAIR DE LUNE ] is the only level with a Skull door requiring more than one Skull to open, and the only instance of multiple Skulls of one color being present.
- [4-3 /// A SHOT IN THE DARK] has a unique Skull with a pink hat on it in The Tomb of Kings. This is the only level with a unique Skull. The Skull is a reference to Matt McMuscles.
- During Halloween, the skulls will turn into pumpkins.
- A purple-colored Skull also exists, appearing upon collection of three skull crates (or an Overheal powerup) in Clash Mode. This is a reference to HerbMessiah, a YouTuber who prominently makes videos on ULTRAKILL.
- There are also textures for a white-colored skull, although they have gone unused as of now.
- If you have no arm equipped, Skulls will become impossible to pick up, which will also make some levels impossible to complete.
- Without an equipped arm, it is impossible to pick up a Skull, even with the Whiplash.
- It is possible to delete a Skull from a level. Simply pick it up, return to a terminal and unequip all of your arms. Upon equipping them again, the Skull will be gone.