Mammon

Mammon is the Second Duke of Hell, whose sphere encompasses betrayal. It is said that he smiles on people who call others freind, only to stab them in the back. Needless to say, with a domain like betrayal, Mammon is the least popular of the Dukes of Hell for conjuring. For his part, Mammon is simply amused by this. Throughout history, Mammon has put his unholy hand into human politics, with the most famous of these interventions being the betrayal of the General-Archmage Kas, when his master, the Mad King Vecna, threatened all of mortalkind with his Eldritch magic and armies of undead. When Mammon was questioned as to why he did such a thing (or, more to the point, why he would do something so benifical to mortals) Mammon simply replied that mortals were an interesting source of amusement, and that their souls were like his, in the end. Mammon is sealed on the level of Baator known as Cania, where no light pierces the darkness, and where the victem cannot see the murderer.

Summoning
In order to summon an avatar of Mammon, a magical dagger must be drawn on the ground. In the center of this dagger-drawing, two real daggers must be placed, along with a scap of the conjurer's clothing, and one day's trail rations. The final ingrediant is the blood of an ally (in this case, a party member or the closest thing to a party member that is on hand). Then, the following incantation must be chanted:

"Mammon, I summon thee, lord of the dark, and Prince of Hell! I call you to me, not that I might place steel through your chest, but that I might serve thee, as freind to freind. Betray not me, lord of betrayers! Use me as you would the dagger that pierces your foe's heart. I bend my knee to thee, for your blessing!"