Ambrosia is an Artifact that can be rarely found as a room clear reward. It can be given to characters to improve your relationship with them and in most cases earn Keepsakes. (Hades is a jerk and will not give a Keepsake when given Ambrosia.)
||'...The food of the gods is the Underworld's number-one delicacy, and truly perhaps one of the only sources of genuine lightness here within this realm. How the substance came to be here is unclear to me, though even I have something of a taste for it by now, based on the few occasions when I've had the chance to try it for myself. Everyone I know in the Underworld, irrespective of their disposition, categorically enjoys the stuff. It is a prized possession, and anyone who would offer it up willingly does so genuinely as a friend.'