

They may also contain Signs of the Zodiac. Planetariums are similar to Treasure Rooms, but only contain special astronomy-themed items that are only available through Planetariums. These rooms also have an individual chance to spawn in the purple-tinted areas of the Mausoleum, without Isaac previously skipping any Treasure Rooms. If Isaac enters a Planetarium, the chance will be set to 0% and can't be increased again This chance is further increased by an unknown percentage if Isaac has Magic 8 Ball or Crystal Ball. The Treasure Room must not be entered at all to be considered skipped. The chance for a Planetarium to appear starts at 1% and will increase by +20% whenever a Treasure Room is skipped. These items include the Signs of the Zodiac, Tiny Planet, Magic 8 Ball, and Crystal Ball. Planetariums are unlocked by possessing three astrology-related items simultaneously. Like Treasure Rooms, they require a key to enter. The Planetarium is a new unlock-able room type introduced in Antibirth that has a small chance to appear after certain criteria are met. For a list of other rooms featured in Antibirth, check out Chapters.
