The Mortal Potion is a glowing pink, poison-like potion that makes the drinker mortal (hence the name, as it is used on immortals). It is used by Pain and Panic to make Hercules drink it and become mortal.
Hades concocts a potion to make baby Hercules mortal so that he can kill him. Hades instructs his sidekicks, Pain and Panic, to administer the potion to Hercules. Hercules becomes mortal, though keeps his godlike strength, as he does not drink the last drop. Pain drops the bottle when he and Panic hear Amphitryon and Alcmene coming, and the bottle breaks.