Frostlight, Shard of the Night Walker

FROSTLIGHT, SHARD OF THE NIGHT WALKER

Weapon (Stave) Legacy Weapon (Requires Attunement by a Warlock) Can be used by an arcane focus.  

Backstory
The Frost Wardens were a select group of warriors trained to be paragons of their craft. Warlocks, Sorcerers, Warriors, Rangers, and so on each trained to be "Exarchs" of their devotion and sought the title of "Exarch". The Frost Wardens formed a court of the finest warriors and wizards who would be tasked with duties above and beyond those tasked to even the bravest of Fey warriors. A collective of Fey Nobles all skilled in the arcane arts bonded themselves to a demon from a chaotic plane. The demon gave them the ability to create items of power which shook the very foundations of Fey culture. This collective, known as the Order of Winter's Touch, crafted weapons for the Frost Warden with a special power imbued into them. They were each given an artifact which granted them the power to ignore the binding tenants of the Unseelie Accords. This made them incredibly dangerous as they could perform even basic activities which were impossible to normal Fey, such as the simple act of lying. This also allowed them to strike at the Court of Summer without fear of reciprocity. In exchange for this power, the Order of Winter's Touch had unknowingly bound themselves to this Demon Lord and were drawn into it's plane of existence to a fate unknown. The Frost Wardens, free of their former shackles, began to strike at the Court of Summer. With the pillars the Feywild now rocking from the imbalance, The Queen of Air and Darkness herself discovered this sorcery and ordered the Frost Wardens killed before they overturned the entire plane in their conquest against their eternal enemy. Vanquishing the Frost Wardens turned out to be more of a difficult task than originally expected. Without the Unseelie Accords to bind them and with their aptitudes as warriors these 12 warriors proved to be incredibly deadly. Hundreds of Fey Champions and Knights were slain in the pursuit of this order. At the order of Queen Mab, their weapons, their items of power were destroyed on sight. After a century of pursuit, all but one of the Frost Wardens was slain. 

Ereykos Daaris, known as the "Night Walker" was the Warlock Exarch in the Order of the Frost Wardens. A particularly cunning spellslinger, the Daaris was able to evade capture. Finally, after one grueling battle, a stray crossbow bolt caught Daaris in the shoulder. Realizing he was about to be overwhelmed he banished his weapon to another plane, a final insult to the Queen herself. 

No one knows how Mavis found the unshackled item or if the weapon she gifted to her champion Alderoc was more than a replica of the fabled blade. Agents of Summer report the Lady of Winter refuses to let the Warlock bring the weapon into the Feywild, an odd request given her sheer power within her domain. Some even whisper that the mysterious Champion of Winter Alderoc is actually Ereykos Daaris, a peculiar notion; however, the body of the rogue warlock was never actually seen or produced...but only reported to the Court of Winter. The question remains, why would Mavis want such a dangerous Fey in her service at all, an individual able to usurp the balance of power within the plane itself.  

Character Level/Rarity	Abilities
1/Common	The wielder is resistant to cold damage.  Frost Blade. You can use a bonus action to create of dismiss a blade of cold energy to extend from the head of the staff making the staff look like a scythe and causing it to deal slashing damage instead of bludgeoning damage. While active, attacks made by the weapon deal an additional 1d6 cold damage.   Feature:  When you wield this weapon, small wisps of winter swirl around the head of the weapon. If the wielder stands still with the weapon attuned and at the ready, the weapon's core will begin to glow a dark blue and snow flakes will fall around the wielder.
5/Uncommon	The wielder has +1 to attack and damage rolls.  The wielder must attune to Frostlight, Shard of the Night Walker at this rarity and higher.
9/Rare	Frost Carver. The frost blade grows in size and now deal an additional 1d8 cold damage.
13/Very Rare	The wielder gains +2 bonus to attack, damage, and spell rolls made with Frostlight, Shard of the Night Walker Winter's Touch. Once per turn, when you kill one or more creatures with this weapon or a warlock spell, you regain 4 hit points as the cold of winter seeps into your enemies. You don't gain this benefit for killing constructs or undead.
17/Legendary	The wielder gains +3 bonus to attack, damage, and spell rolls made with Frostlight, Shard of the Night Walker Frost Scythe. The frost blade grows in size and now resembles a large icicle of dark blue. The weapon now deals an additional 1d12 cold damage. Winter's Embrace. Frostlight, Shard of the Night Walker now holds 20 charges and can be used to cast Otiluke's Freezing Sphere at 6th Level for 6 charges with every additional charge counting as a spell slot (i.e. 7 charges to cast a 7th level invocation). The head of the staff is the origin for the spells and the wielder is not affected by the sphere while holding the weapon. When a creature (with CR level decided worthy by GM) is killed by the Sphere their soul refuels the staff with 2 charges. The staff regains 1d8+5 charges at dusk.