Urschleim

Urschleim is an optional end-game boss found in the Passage. It is a gigantic slime-like mass that stretches across the biome and slowly moves clockwise along a fixed route. When it is nearby, the player can hear a loud rumbling sound and the screen begins to shake, which serves as a warning that it is approaching.

Urschleim can be located with an Urschleim Scanner, and after it is defeated it can be summoned again anywhere in the Passage by using a Primeval Slime Cell. It travels through obstacles without destroying them, so its movement is not stopped by terrain or structures in its path.

Combat against Urschleim is centered on its three glowing bulbs. Its outer shell cannot be damaged, and attacks from behind are ineffective for most weapons because short-range attacks cannot reach and long-range attacks are deflected or dissipate on impact, as if they had struck a block. Once the three bulbs on its front are destroyed, its head becomes vulnerable for a short time. During that window, the head can be damaged before it retracts, the bulbs respawn, and the cycle repeats until the boss is defeated.

A few important details make the fight work differently from many other bosses:

• Urschleim does not have a normal attack pattern, but touching it instantly kills the player.
• Its vulnerable damage is soft-capped at 25% of its maximum health per cycle, so the bulbs must be destroyed at least four times to finish the fight.
• If the player dies during combat, Urschleim’s head returns to full health, but the bulbs do not, which can affect how the fight continues after a death.
• The boss moves in a consistent clockwise pattern, so ranged weapons are especially useful for hitting the glowing bulbs while staying out of contact range.
• It is helpful to clear a long path through the Passage or memorize the natural route through the biome so the player is not trapped or caught by its movement while fighting.

Urschleim’s name is German and means “primordial slime” or “original slime.”