Kharitite

Kharitite, also known as Joy Beasts or Empathy Beasts, were a species native to the planet Vreular in the Fifth Galaxy. They biologically converted negative emotions into mass energy and fed on them, allowing them to take away emotional pain and frustration. (COMIC: After Life)

Biology
Kharitites vaguely resembled rainbow coloured dogs and behaved in much the same manner. However, what appeared to be a tail on their bodies was actually a feeding tube that absorbed negative emotions from the atmosphere a Kharitite was in. The more negative emotions they ate, the larger their physical size increased. (COMIC: After Life)

Behind the scenes

 * Kharitite is used as an enemy in Doctor Who: Legacy mobile game.