Wondrous Item, artifact (requires attunement by a By a worthy hero of the realm, must be a Barbarian, Fighter, or Paladin)
The Amulet of the Plane of Fire is a golden chain with an extremely powerful elemental gem at the end. It has the powers of a normal fire elemental gem, but the summoned beings have 10 more hit dice, all the damage is multiplied by two, and they are huge. Along with that, the amulet can cast a 10d6 fireball (uses a charge) and can cause the wielder's weapons to do an extra 3d6 fire damage. The amulet is sentient, and has an alignment of chaotic good. On top of that, it sets the wielder's strength to 19. It will give encouragement to the wielder during battle, giving +3 on to hit rolls.
Notes: Bonus: Ability Checks, By a worthy hero of the realm, must be a Barbarian, Fighter, or Paladin, Teleportation, Combat, Jewelry, Outerwear, Sentient