Of all the magic items created by the elves, one of the most prized and jealously guarded is a moon blade. In ancient times, nearly all elven noble houses claimed one such blade. Over the centuries, some blades have faded from the world, their magic lost as family lines have become extinct. Other blades have vanished with their bearers during great quests. Thus, only a few of these weapons remain.

A moonblade serves only one master at a time. The attunement process requires a special ritual in the throne room of an elven regent or in a temple dedicated to the elven gods.

A moonblade won't serve anyone it regards as craven, erratic, corrupt, or at odds with preserving and protecting elvenkind. If the blade rejects you, you make ability checks, attack rolls, and saving throws with disadvantage for 24 hours. If the blade accepts you, you become attuned to it and a new rune appears on the blade. You remain attuned to the weapon until you die or the weapon is destroyed.

A moonblade has one rune on its blade for each master it has served.  

Rune Abilities

1. The first rune is crimson with the elven symbol of Strength. (Adds +3 to damage and attack rolls) 
2. The second rune glows with strong fey magic with the eleven symbol for Ally. You can use an action to call forth an elf shadow, provided that you don't already have one serving you. The elf shadow appears in an unoccupied space within 120 feet of you. It uses the statistics for a shadow, except it is neutral, immune to effects that turn undead, and doesn't create new shadows. You control this creature, deciding how it acts and moves. It remains until it drops to 0 hit points or you dismiss it as an action.
3. The Third rune glows silver with the elven symbol of Furry. The moon blade scores a critical hit on a roll of 19 or 20.
4. The Fourth Rune glows green with the elven symbol for Guardian. The item whispers warnings to its bearer, granting a +2 bonus to initiative if the bearer isn't incapacitated.

Once per round, when you hit a creature with an attack using this magic weapon, you can wound the target. At the start of each of the wounded creature's turns, it takes 1d4 cold damage for each time you've wounded it, and it can then make a DC 15 Constitution saving throw, ending the effect of all such wounds on itself on a success. Alternatively, the wounded creature, or a creature within 5 feet of it, can use an action to make a DC 15 Wisdom (Medicine) check, ending the effect of such wounds on it on a success.

Once per long rest, as a bonus action you can cast the Mass Healing word spell at 4th level. Your spellcasting ability modifier for this is Wisdom.

Proficiency with a Longsword allows you to add your proficiency bonus to the attack roll for any attack you make with it.

Notes: Damage: Necrotic, Damage, Combat, Versatile, Sap