User can possess or take over the body of any living being, whether sentient or not, by stealing their motor functions and senses. Users may or may not have to leave their own body for this to take place. Disembodied users such as spirits may use the body as their own.
Temporarily/permanently inhabit the body of the target.
Take complete control of a target's body, even using it as your own (the target is then known as a vessel).
Control a person's actions.
The user's mind/spirit/soul can leave their body freely.
Skilled users can possess multiple host bodies while retaining their own or even while occupying another vessel.
When the user possesses a body, they gain the skills and powers of the body.
Can possess a body which can be useful for espionage and can lie dormant inside the person's mind and body.
Utilize as a last resort to escape a dying body and to achieve immortality.
The overshadowed being might be able to fuse with them creating a new being.
A.D.A.M. (Archie's Sonic the Hedgehog) possessing the body of Tommy Turtle.
Jericho (DC Comics) can only posses individuals via eye contact.
Daniel Kilgore (Image Comics) can only transform into Haunt when the ghost of his dead brother Kurt Kilgore possesses him.
The entity known only as Malice (Marvel Comics) possessing Alex Summers/Havok.
Chthon (Marvel Comics) possessing Quicksilver.
Agamotto (Marvel Comics) was capable of possessing powerful mages such as Daimon Hellstorm...
....and superpowered beings like the New Avengers.
Kuurth, Breaker of Stone (Marvel Comics) possessing The Juggernaut during the Fear Itself event.
Xi'an Coy Manh/Karma (Marvel Comics)
Following his death on Mustafar, Lord Momin's (Star Wars) essence inhabited his mask, allowing him to possess anyone who wears it, including an Imperial lieutenant...
...and his own resurrected body.
The ancient sith Karness Muur (Star Wars Legends) used the Force to seal his soul in the Muur Talisman before his first death, allowing him to possess anyone who wore it so long as their will wasn't strong enough to resist his own, as was the case with his longest host, Celeste Morne.
The Transcendent Naphalem Genesis (Vertigo Comics) possessed Reverend Jesse Custer during his last sermon, causing a massive explosion that killed everyone inside the church except for Jesse, who emerged from the demolished building without a single injury.
The Red Blood Queen of Hearts (Vampirella) is a cultist of the demon god Chaos whose soul was trapped into a playing card, forcing her to possess any mortal woman who touches the card to regain a physical form.
A demonic hyena (Buffy the Vampire Slayer) possesses a group of students.
The Beast (Doctor Who) possessed Toby Zed so he could escape Krop Tor ...
... and possessed Sanctuary Base's Ood as well to act as his Legion.
An Eight leg (Doctor Who) possesses Sarah Jane.
The Mara (Doctor Who) has possessed Tegan on various occasions.
Louie Preston (The Haunted Hathaways)
Miles Preston (The Haunted Hathaways)
Luke and Emma (Jessie) being possessed by evil spirits.
Erick (Los Protegidos) can possess any body.
Androvax (Sarah Jane Adventures) possessing Sarah Jane Smith.
Countess Margaret Isobel Thoreaux (Smallville) possessing the body of her descendant Lana Lang.
Anubis (Stargate SG-1) has no body and uses a human-shaped force-field to keep his energy form intact. Without it, he can possess any human and use their body as his own, but the body will decay as a result of holding him.
The Leviathans (Supernatural) possessing Castiel and his vessel, Jimmy Novak.
Lucifer (Supernatural) possessed Nick, his plan b vessel...
....but because Nick is not his true vessel, his body decayed from Lucifer's sheer power.