Weapon (longsword), unique (requires attunement)
The hilt of this longsword is obsidian wrapped with overlapping dark leather. The blade seems charred and smells faintly of sulfur. Dark runes are etched on the blade. The blade also feels quite warm to the touch.
The runes are in Suloise, and read Fireheart. The leather of the hilt is made of hell hound hide.
Even when you are not attuned to Fireheart it counts as a magic weapon and deals an additional 1d8 fire damage on a successful hit.
If you are attuned to Fireheart and have it on your person, you have resistance to fire
For any effect that requires a spellcasting ability check, use a +4 for this check, unless you own is better.
Fire Magic. Any fire-based spell or effect you cast gains a +1 to any attack roll required as well as to any spellcasting check and save DCs. Each damage dice of a fire-based spell or effect you cast gains a +1 to it.
Blade of Fire. You can use a bonus action to speak the Fireheart’s name, causing the dark runes to flare and burn bright white and covering the blade with blue flames. These flames shed light in a 40-foot radius and dim light for an additional 40 feet. The flames last until you use another bonus action to speak the command word again or until you drop or sheathe the sword. The flames do not increase the fire damage dealt by the weapon, as it is now just externalizing it heat.
Counter Cold Effect. As a reaction, while wearing Fireheart you can attempt to counter any spell, psionic power or similar effect that deals cold damage that has you in its area of effect as if you cast counterspell with a 6th level spell slot and a spellcasting ability of +5, except that its effects extend to other supernatural effects. For effects that do not have a spell slot (or equivalent), such as a dragon’s breath weapon, make a spellcasting ability check using the Save DC of the effect as the DC of the check. Once used this property cannot be used again until an hour has past, and shares a recharge with Banish Cold_.
_*Banish Cold.* As a bonus action, you can plunge the sword into any nonmagical ice or similar area, melting the ice and cold within 20 feet of Coldheart or portion of the fire if it is larger. You can also use this to attempt to dispel magical, psionic or similar coldeffects as if you cast dispel magic with a 6th level slot, except that its effects extend to other supernatural effects. Once used this property cannot be used again until an hour has past, and shares a recharge with Counter Cold Effect.
Paired Set. Fireheart is paired in a set with the sword Coldheart . When both weapons are attuned to and wielded, it gains additional features.
The additional fire damage is increased to 2d8.
Spellcasting ability check increases to +5.
The spell slot cast for both Counter Cold Effect and Banish Cold increases to 7th level.
Any object or construct that suffered both fire and cold damage from both weapons suffers an additional 2d8 magical bludgeoning damage.