Skull Keys

SKULL KEYS
MercurySulfurSaltBlue (old)Red (old)Purple (old)
Appearances
0-2 1-1, 1-2, 1-3, 1-4 2-3, 2-4 4-2, 4-3, 4-4 5-1, 5-2, 5-3 6-1 7-1, 7-2 0-E, 1-E P-2

Skull keys are a commonly recurring item in ULTRAKILL that primarily act as keys to open locked doors. First present via a secret in 0-2: THE MEATGRINDER and introduced proper in 1-1: HEART OF THE SUNRISE, they can be found in both blue and red colors, denoting compatibility with same-colored pedestals. Many level progressions throughout ULTRAKILL revolve around locating and retrieving skull keys in order to open the path forward.

To pick up or place down a skull key, the player must punch it with any arm, including the Whiplash's hook. Skulls can only be set down on pedestals.

Skull keys are obtained from altars, also referred to as pedestals. When placed down on an empty altar of the same color as the skull, it may activate or open something within the level, generally a door near the player. Skulls placed down on their respective altars glow white from the symbols on their foreheads. Altars can be distinguished from their colors, symbols and shapes: blue altars fill with mercury around the blue skull when activated, while red altars ignite embers around the skull. Altars which hold other Held Objects are white and fill with salt when activated. Encore levels feature modified metal altars that require the player to stand in front of them to open and access.

While holding a skull key, the player's off-hand will be held up to be visible on the screen and show the skull in their hand. This is only cosmetic however, as the player will remain able to punch, parry, throw coins, and do any other usage the off-hand may have. If the player throws their Whiplash, the skull key will be attached to the tip of the spearhead. If the player punches or hooks an enemy while holding a skull key, the enemy will catch on fire if it is flammable or is coated in Gasoline.

Skull keys constantly emit a faint glow, which may prove helpful in dark environments such as 0-S. This light will become much brighter if the player punches while holding the skull key, but this intensity will fade back to its default state over a short lapse of time and require some time before it can brighten up again.

In 4-3, a blue skull key with the hat of Youtuber Matt McMuscles can be found as part of the Tomb of Kings secret.

In 7-1, the player finds a red skull resting where the head of a beheaded Mannequin would be. If they are to place on the Mannequin a blue skull found later in the level, a wall in the corner of the room will slide open, allowing access to a secret corridor that leads to the secret boss of the level.

Media

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  All Skulls and Altar states.
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  Picking up a skull key.
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  Putting down a skull key.
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  Picking up a skull key using whiplash.
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  Putting down a skull key using whiplash.
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  A statue of a Ferryman with a "Salt" skull key.
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  Stained glass windows depicting the "Sulfur" and "Mercury" skull keys.
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  The Blue Skull of Matt McMuscles.

Trivia

• Skull keys are strongly implied to be the heads of deceased Ferrymen, the keys' latent power a byproduct of the divine energy they are exposed to throughout their afterlives. This is mostly evident in the lore entries for the Ferrymen.
• The symbols that appear on the blue, red and white skulls are the alchemical symbols for mercury, sulfur, and salt respectively. These three elements were treated as the Tria Prima or the Three Primes, which were believed to be foundational elements in alchemy.
• While blue and red are the only colours of skull key found in the main game, several more exist in secret levels.
  • The texture of the Cancerous Rodent and Very Cancerous Rodent is the regular old skull texture hue-shifted to green.^[1]
  • A purple skull can be acquired in 4-S: CLASH OF THE BRANDICOOT if a Protector Crate is collected while two skull power-ups are already active.
• In 1-4 and 5-3, attempting to put down a blue skull key on the missing head of the beheaded sinner's skeleton and beheaded Rocket Launcher-wielding Ferryman will place the skull where their head would be and show a comedic secret message. This does not affect how these levels play out.
  • In 1-4: CLAIR DE LUNE:
    Nothing happens, but you feel a strange satisfaction
    You decide to name it Hank.
  • In 5-3: SHIP OF FOOLS:
    Nothing happens, but you're sure Hank Jr. and his Hankcestors would appreciate it... if they weren't dead.
• Attempting to Whiplash a skull key from behind the door it opens will cause the doorway to flash red with a unique sound effect, leaving behind the skull and displaying the following message:

ERROR: BLOCKING DOOR WOULD CLOSE