You can spend 10 minutes to perform a ritual to reach across the boundaries of the world to call forth a companion. At the end of the ritual, the creature appears in an unoccupied space that you can see within 10 meters and assumes the form of a companion based on your origin. Subtract an amount of mana equal to your mana limit each time you take a rest. Your eidolon is augmented to that amount of mana.
Your eidolon bears a glowing rune that is identical to a rune that appears on your forehead as long as your eidolon is summoned. While this rune can be hidden through mundane means, it cannot be concealed through magic that changes appearance, such as shapechange or polymorph (although invisibility does conceal it as long as the spell lasts).
As an action on each of your turns, you can mentally command your eidolon if it is within 100 meters of you (if you control multiple creatures, you can command any or all of them at the same time, issuing the same command to each one). You decide what actions your eidolon will take and where it will move during its next turn, or you can issue a general command, such as to guard a particular chamber or corridor. If you issue no commands, your eidolon only defends itself against hostile creatures. Once given an order, the creature continues to follow it until its task is complete.
If your eidolon is ever slain, the magical bond you share allows you to return it to life. With 8 hours of work and the expenditure of 25 sp worth of rare materials, you call forth your eidolon’s spirit and use your magic to create a new body for it. You can return an eidolon to life in this manner even if you do not possess any part of its body.
Your eidolon appears in a form based on your origin.
Aberrant. Your eidolon is an aberration, but uses an animal form. It has advantage on saving throws against spells and other magical effects.
Arctic. Your eidolon is an elemental: an ice elemental
Astral. Your eidolon is any companion form you choose. It no longer needs to breathe and it has advantage on saving throws to avoid being charmed or sent to another plane.
Beholder. Your eidolon is any companion form you choose.
Celestial. Your eidolon is a celestial, but uses an animal form. It gains resistance to radiant damage and has advantage on saving throws against being frightened.
Chaotic. Your eidolon is any companion form you choose.
Draconic. Your eidolon is a Dragon.
Fey. Your eidolon is one of the animal or fey forms.
Fiendish. Your eidolon is a fiend, but uses an animal form. Magical darkness doesn’t impede its darkvision. It gains resistance to fire and poison damage.
Genie. Your eidolon appears in an elemental form based on the type of genie you originate from. Dao: earth elemental, Djinni: air elemental, Efreeti: fire elemental, or Marid: water elemental.
Mummy. Your eidolon is an elemental: a sand elemental.
Phoenix. Your eidolon is a phoenix.
Sea. Your eidolon is an elemental: a water elemental.
Shadow. Your eidolon is an undead: a shadow, but uses an animal form. It has a shadowy form which allows it to enter a hostile creature’s space and stop there. It can also move through a space as narrow as 2 centimeters wide without squeezing and once on its turn while in dim light or darkness, your eidolon can use Stealth without using an action.
Spectral. Your eidolon is an undead, a ghost or specter, but uses an animal form. It can move through other creatures and objects as if they were difficult terrain. It takes 5 (1d10) force damage if it ends its turn inside an object.
Stone. Your eidolon is an elemental: an earth elemental
Storm. Your eidolon is an elemental: a lightning elemental.
Vampiric. Your eidolon is an undead, but uses an animal form. It has the Blood in the Water maneuver and it has resistance to necrotic damage.