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The Planetarium is a new unlockable room type introduced in Antibirth that has a small chance to appear after certain criteria are met. Like treasure rooms, they require a key to enter.

Planetariums are unlocked by acquiring three astrology-related items in a single run. These items include the Signs of the Zodiac, Tiny Planet, Magic 8 Ball, and Crystal Ball.

The chance for a Planetarium to appear starts at 1% and will increase by +20% whenever a Treasure Room is skipped. The treasure room must not be entered at all in order to be considered skipped. This chance is further increased by an unknown percentage if Isaac has Magic 8 Ball or Crystal Ball.

These rooms also have a chance to spawn in the purple-tinted areas of the Mausoleum, without Isaac previously skipping any Treasure Rooms.

Planetariums are similar to treasure rooms, but only contain special astronomy-themed items that are only available through Planetariums. They may also contain Signs of the Zodiac.

If a planetarium spawns on one of the alternative floors where treasure rooms would normally have 2 items to choose from, the Planetarium may still have only one item with no alternative choice available.

Planetarium Items[edit | edit source]

Name Icon Description
SolSol Icon.pngActivates the Sun tarot card and fully recharges Isaac's active item upon defeating a boss. Reveals the location of the Boss room on the map.
LunaLuna Icon.pngAdds one extra Secret Room and one Super Secret Room on each floor.
MercuriusMercurius Icon.pngDoors stay open after entering a room, even with enemies in it, allowing Isaac to leave any time. Increases speed.
VenusVenus Icon.pngEnemies near Isaac will be inflicted with Charm that wears off quickly after enemies move away from Isaac, causing enemies to attack each other.
TerraTerra Icon.pngIsaac's tears become rocks. The tears can also destroy rocks.
MarsMars Icon.pngGain the ability to charge by double-tapping in a direction. Isaac is invincible during the charge and deals significant damage. Can be used multiple times per room with a short recharge time.
SaturnusSaturnus Icon.pngIsaac is surrounded by an aura which grants 7 orbiting tears when entering a new room and has a chance to absorb incoming enemy tears.
UranusUranus Icon.pngIsaac shoots ice tears.
PlutoPluto Icon.pngDecreases Isaac's size to the point where many tears will fly over Isaac. Increases tears and speed, and decreases range.