Felix Felicis

Felix Felicis is a potion that is Lady luck in liquid form. It is a golden liquid. Felix Felicis makes the drinker lucky for a period of time, dependent on how much is drunk, during which time everything they attempt will succeed. It must be used sparingly, however, because if taken in excess it causes giddiness, recklessness and dangerous overconfidence. It is highly toxic in large quantities, and is also a banned substance in all organised competitions such as Quidditch,along with all other methods of cheating. It is very difficult to make and must stew for six months before it is ready to be drunk.

In Harry Potter and the Half-Blood Prince, Harry Potter wins a small vial of Felix Felicis from Professor Slughorn for completing his potion, correctly, first. He later offers a small amount to Ron Weasley so that Ron can feel more confident about his Quidditch playing. Ron plays a near perfect game, and Harry later tells him that he didn't give him the potion at all, and that Ron played that well all by himself. The potion is later used in attaining an important memory from Slughorn, and in a the battle against Death Eaters invading Hogwarts.

Felix Felicis possibly works by providing the drinker with the best possible scenario from thousands. This usually registers in the drinker's mind as an unusual urge to do a certain action, or as a voice telling him to do so. The effectivity of the potion thus depends on the cooperation of the drinker with the voice, for the drinker may choose not to obey whatever the voice tells him to do. This is easily remedied, however, as the potion does not single out only one scenario, but changes paths as the situation unfolds.

The effectivity and actions of Felix Felicis in time travel are yet unknown.