The Mystic Ambit Incant is an artifact in Hexen. It is a scroll with a blue rune on it, and activating one has a different effect depending on which class is using it.
The Fighter gets a temporary boost of one point to his armor class.
The Cleric regains a significant portion of his health, if injured.
The Mage gets more Mana. If the player can have any more Blue Mana, it fills that first, and then gives the remainder in Green Mana.
The effect will also be applied to all nearby players in co-op, thus it makes sense to gather together when using the Incants to get the most of them. Perhaps because of this multiplayer nature of the item, Incants, at least in the original game's maps, do not appear in single player.