- You may be looking for the entity from Shadowmind.
The Umbra were a group of intelligent psychic predators who "[thought] as one" and devoured their victims, using the empty shell as a vehicle to move in.
The Umbra were pitch black in appearance, and had a perpetual grin on their faces. They took the form of humanoids, such as humans and a species native to another planet. They were at least partially made out of "psychic fabric", but could also produce tendrils to grasp their prey. (COMIC: The Eye of Torment)
The Umbra were attracted to emotions like self-loathing, pain, shame, regret and guilt to feed off so that they could "devour" people's minds and souls. They could also use mind control on people and broadcast psychic messages. They could fly in space and appeared to have survived in the Sun's chromosphere for "millions of years". According to the Twelfth Doctor, particle beams "probably taste[d] like Weetabix" to them, although they could be stopped by low temperatures. They could also swarm together and anchor objects to larger bodies of mass, including the Pollyanna, which was shielded against the gravitational force of the Sun. (COMIC: The Eye of Torment)
When the Sun was a "young star", a scientist created a psychic fabric that was capable of removing the pain that lay in all living beings. He fashioned it into a cloak and named it "the Umbra". However, the Umbra gained intelligence and "became alive", killing people all over the planet, devouring their forms, spreading and multiplying. The scientist, whose guilt was so great that he could use himself as bait to draw the Umbra together, brought the Umbra into the Sun, using what the Twelfth Doctor assumed was a trans-warp tunnel powered by the Sun. The Umbra survived their trip, however. Sandy Tanaka guessed the Umbra had been swimming through the Sun's chromosphere for "millions of years". Eventually, the Pollyanna, a sunship on an expedition to circumnavigate the Sun, had reached the Sun's surface. One Umbra snuck in to the Pollyanna via a plasma conduit and used its psychic abilities to convince Georgia Butler to disengage the safety in the plasma room. With the safety disengaged, the plasma burnt Georgia and Harriet Wilcox inside and the Umbra was able to spread and reach the flight deck and navigate Pollyanna back to Earth, killing and taking on human bodies as they did so.
Thousands of Umbra began swarming the outside of the Pollyanna and anchored it to the Sun. As the Umbra reached the flight deck, Clara Oswald destroyed the navigation controls, preventing the Umbra from finding Earth, and the crew headed off to auxiliary control so the crew could navigate with the back-up systems. Eventually the Pollyanna crew were surrounded, and Clara asked the "total narcissist" Rudy Zoom to talk to them. The Umbra inside tried feeding on Rudy's mind, but because he was a narcissist who had no regrets in life, the inside of Rudy's head was "like poison" to the Umbra and the Umbra died. On the outside of the ship, the Doctor was ejected out of a plasma intake by Officers Wright and Jordache to attract the Umbra that had surrounded the ship to his two thousand years' worth of regret. He set up the final link to Professor Alice Dubrovnik's graviton inverter on the hull of the ship, allowing Alice to briefly boost the inverter and create a secondary gravity envelope, which inverted not only the gravity, but the heat as well, freezing the Umbra on the outside to death. (COMIC: The Eye of Torment)