D&D General Solar's Flying Sword as a Legendary Weapon

[Stalker0]

The very quick jist. The party is going to find a solar's flying sword attached to a special stone that can mimic a creature type (think a very power nystul's magic aura). So...the sword believes it is being weilded by a solar.

So treating this as a legendary weapon but it won't do the full damage it does as a solar (that would be beyond nuts). Ok so a straight up dancing weapon is 1d8+ability mod as a bonus action out to 30 feet as a very rare weapon.

The solar's weapon can go up to 120 feet, and I'm trying to think of what radiant damage bonus to add on top to give it the full upgrade to legendary (note there is no +x bonus, so no attack bonus). How much radiant damage do you think is reasonable to get this into a solid legendary weapon without going overboard?

 

[AlViking]

I would compare to other legendary items. A few random examples

1. Dawnbringer has all the properties of a sun blade (+2 weapon +1d8 radiant, sheds sunlight) and can cast lesser restoration once per day.
2. Hazirawn if you're attuned it's a +2 weapon that does an extra 2d6 necrotic damage. It has 4 charges and can cast detect magic, evil and good, thoughts. In addition any creature hit can't regain HP until it makes a DC 15 con save at the end of it's turn.
3. Irongang +2 weapon and extra 1d8 thunder damage, resistance to acid damage and dominate monster on an earth elemental once per day along with tremorsense to 60 feet. On top of that you have 3 charges and can use 1 to cast shatter.

So what I'm seeing is that +2 weapon, 1d8 or 2d6 extra damage (or the damaging spell shatter) along with some other benefits with my admittedly small sample size. So I would consider making it a +2 weapon, +1d8 radiant and pick something that a solar could do like the blinding gaze - although I'd probably tie the save DC to the wielding character's ability score used for the weapon.

Just flying is cool but with no plus and fairly small damage bonus, I see it more as a very rare item than legendary. At least that's my take.