I'm planning on putting this item on a boss NPC my players are likely to encounter sometime soon.. wanted to get ideas on its GP value.
"Soul of Draco"
This jeweled necklace is uncomfortably warm to the touch. When worn, it becomes intensely hot, dealing 1.ire damage per round to the wearer until removed.
Each time the wearer casts a spell with the fire descriptor, she is temporarily sheathed in flame. If she is hit with a melee attack while casting the spell, the attacker takes 1d6 fire damage and must succeed a Reflex save (DC same as the spell) or catch fire (1d4 damage each round until a successful Reflex save negates). For a number of rounds equal to the level of the spell, the wearer gains cold vulnerability and doubles any fire resistence. Melee attacks by the wearer during this period also deal fire damage and ignite the target as above.
After wearing the necklace for a week, the user gains the additional ability to summon a phantasm only he can see of a noble efreet. The summoned efreet is always the same creature and is familiar with the wearer's conduct while wearing the necklace. If the efreet approves, it will lend the wearer its considerable knowledge in the secrets of fire. i
This looks more like a minor artifact to me because of the phantasm. Many of its abilities have no restriction on use and it harms the wearer.
I'd probably price it as a constant fire shield effect (4th level spell). While the item effect is much weaker than fire shield, the phantasm gives it great value. Gaining the loyalty of a powerful outsider while also gaining the ability to communicate with them at will is a very large boon.