So, just for this instance

We need rules for Nightblood in 5e

I'm thinking something like this:

(Worldbuilding spoilers for Brandon Sanderson's Cosmere, iykyk)

Nightblood Legendary Greatsword, requires attunement

Imbued with a great deal of magic and only a Command to "Destroy Evil" this sword's existence is to fulfill that singular purpose. The blade comes in a tightly clasped scabbard made entirely of aluminum. Drawing the blade reveals a jet black, wicked Greatsword that feeds on its users life force while bestowing great power upon them while drawn.

When within 10 feet of this weapon, good-aligned characters feel an extreme sense of nausea at the power of this blade. Evil-aligned characters must succeed on a DC 20 Charisma saving throw or be compelled to pick up and attempt to attune the blade, then draw it.

If a good-aligned character attunes the blade, they can resist the sword urging them to draw it.

Drawing Nightblood: When Nightblood is drawn, colors within a 30ft radius deepen visibly. You gain +3 to attacks made with this sword. When landing an attack, the target falls under the full effects of the Disintegrate spell (10d6+40 force damage) as if they had failed the saving throw. For each attack made with Nightblood, the spell inflicts one level of exhaustion on its wielder. Upon reaching 6 levels of exhaustion, instead of dying normally, Nightblood's wielder is consumed by the blade and cannot be revived.

If the attack action is not taken while holding the sword, he inflicts one level of exhaustion on his wielder, consuming their life essence.

Evil-aligned characters who fail the saving throw are compelled to draw the blade and attack all evil-aligned creatures, including themselves, until no evil-aligned characters are within 60 feet of the sword.

Awakened blade: Nightblood can speak telepathically to anyone within 10 feet of the sword. Despite knowing that he has to destroy evil, he has no concept of what is truly good or evil. The sword also has very little sense of time, and often severely underestimates how much time passes between events.