Constellation cards are secret keys to hidden realms and areas.
There are 12 Constellation Cards, and all of them are found and stored independent of save files. Each has a special function, and collecting all 12 has its own function.
| Name | Appearance | Unlock | Collection | Image |
| Aries | A photo of a young goat in a field of golden flowers | Enables Save Everyone Ending |
Given upon completion of the True Pacifist Route |  |
| Taurus | Delta Rune with a red background | Grants access to New Home's 'room under renovations' | Hidden underneath a large power crystal (1/2) |  |
| Gemini | A photo of a kid in a striped shirt | Grants access to the Gemini room in the Dev Apartments | Found in the patch of golden flowers in the Caverns after True Pacifist |  |
| Cancer | Has 'Don't make fun of me' scratched on the back | Grants access to Sans' basement | Hidden underneath a large power crystal (2/2) |  |
| Leo | It's swipehole looks like a swirling vortex of fire | Grants access to Zone Zero (required for True Pacifist) | Alphys gives this to you during her date (if you don't have it) |  |
| Virgo | Delta Rune with a blue background | Grants access to the Caverns' 'room under renovations' | Hidden in Toriel's room |  |
| Libra | There is a signature on the front face of the card, it's extremely rigid. | Grants access to Arial's room | Hidden in Zone Zero |  |
| Scorpio | This card's swipehole ends in the shape of a bent hook, with a star in its grasp | Enables the first part of the Bedtime Story |
Hidden underneath the sheets covering Toriel's throne |  |
| Sagittarius | Advertisement for MTT XXL Pro-Blasters | Grants access to So Sorry's art class at MTT Resort | Purchase at MTT Resort |  |
| Capricorn | This card's swipehole vaguely represents the word 'AURORA’ | Grants access to Room 274, accessible within Aurorafall | On display near the counter of the Dev Apartments |  |
| Aquarius | Has a crude drawing of an onion monster on the back. | Has no function | Draw up the fishing pole in Starrin' a third time. |  |
| Pisces | A "Happy Birthday" clip art has been printed on it. | Grants access to the Dev Apartments | In Sans's basement |
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| All collected | Enables the second part of the Bedtime Story |