You have damage resistance to Cold, Fire, Acid, Thunder, and Lightning, as well as immunity to Necrotic and Poison damage due to your wispy presence. On top of this, you have the been quite literally through Hell and back, or in this case Therosi hell, and therefore have immunity to the Charmed, Petrified, Frightened, Grappled, Paralyzed, Poisoned, Prone, and Restrained conditions.

You are able to see in black and white while in the dark to a range of 60ft.

You may move through objects and creatures as if they were difficult terrain. Ending your turn in a square occupied by an object or creature causes you to be pushed to the nearest unoccupied square and take 1d10 force damage.

The eidolon has advantage on saving throws against any effect that turns undead.

A creature receives the same ability score improvements it would have had during its life. Choose a race that you used to be, long ago.

Your strength is set to 7. Your Charisma get a bonus of +3.

While within 10 ft. of your anchor, you are able to move at your proper speed. Each 10 feet further you move from your anchor, your speed is reduced by 10 ft, unless moving directly towards your anchor, until eventually reaching zero and being forced to return to it.

You have the ability to possess a living host or construct and use their body. As an action, you can enter the space of another creature and then attempt to possess them. A willing creature will allow you to enter them immediately. An unwilling creature will have to succeed a save against 8 + your proficiency bonus+ your charisma modifier. You gain their physical stats, such as Strength, Dexterity, and Constitution, but retain your mental traits, such as Intelligence, Wisdom, and Charisma. You are able to use any of its actions, bonus actions, or reactions, but no spellcasting, or any legendary actions or resistances. For an unwilling creature, this lasts for 5 minutes, after which time they are able to make another save with advantage. For a willing creature, this can last as long as you wish, or until they choose they would like it to end. At that point, the creature can make a save against the save DC for unwilling creatures, with advantage if they have been possessed for over 5 minutes. A creature that is possessed can use all of their senses, but is unable to take any actions. If the possessed creature reaches 0 hit points, you are ejected out of its body and are rapidly brought back to your own if over your movement speed away from it. Any damage over 0 transfers over to you upon being ejected. If the host is your anchor, you are able to enter it with 5 feet of movement or a bonus action while within 5 ft., but leaving any host takes a bonus action.

This trait can only be used once per long rest, unless used on your anchor, which takes no action.

Undead are immune to this ability. Any creature with a Charisma higher than 20 is immune to this ability. Constructs have advantage against this ability.

Your AC is set to 9.