Possession

Possession was the act of one being taking over the body and mind of another.

Examples of Possession

Fenric possessed Doctor Judson and Captain Sorin, allowing him a direct hand in his revenge against the Seventh Doctor. (DW: The Curse of Fenric)
The Beast possessed Toby Zed, giving him the ability to breathe fire and survive in areas without oxygen. (DW: The Impossible Planet / The Satan Pit)
The Torajii sun possessed Hal Korwin and Dev Ashton, giving them the ability to vaporise a being by looking at them. (DW: 42)
The Isolus possessed Chloe Webber, giving her the ability to make drawings come to life and living things become drawings. (DW: Fear Her)
Cassandra O'Brien possessed Rose Tyler, when she decided she needed a new human body. (DW: New Earth)
The Bane possessed humans who consumed Bubble Shock!, turning them into zombies at their command. (SJA: Invasion of the Bane)
The Family of Blood possessed 4 humans, giving the Family non-gaseous bodies to travel around in. (DW: Human Nature / The Family of Blood)
The Gelth possessed dead humans, giving the Gelth bodies to use as 'vehicles'. (DW: The Unquiet Dead)
The Midnight Entity possessed Sky Silvestry, giving her the ability to steal the voices of others. (DW: Midnight)
The Psionovore Marchosias possessed Senator Waldo Pickering, giving him superhuman strength and allowing him to directly feed on others' fears. (BFA: Minuet in Hell)
The Pandora entity possessed Inquisitor Darkel's mind, killing her. She had previously occupied other host bodies, but she had always been driven out. (BFG: Gallifrey)