Maelstrom

Greatsword, Very Rare, Requires attunement by a spellcaster   This greatsword grants a +1 to attack rolls and damage rolls on attacks made with this weapon   While attuned to this weapon, you are considered proficient with it and can can use it as a spellcasting focus for your spells. Additionally, you can spend a bonus action and sacrifice a spell slot of 1st level or higher to imbue the blade with nature's wrath for 1 minute. Doing so will cause it to deal an additional 1d4 cold damage and 1d4 lightning damage with each successful attack made with this weapon. If you use a spell slot of 4th level or higher, you use a 1d6 to determine the additional cold and lightning damage, instead of a 1d4.   As an action, you can force your will on Maelstrom's form, temporarily splitting it down it's length into two smaller blades, each of which you are proficient in, have the Finesse trait, and deal 1d6 slashing damage. The act of separating the blades in this way requires your concentration, as if on a spell. However, while the blades are apart in this fashion, you can wave them, to perform the somatic components of your spells and the damage bonuses applied when sacrificing your spell slots affects attacks made from either blade, as your magic imbues both of them.