Wondrous Item, very rare (requires attunement)
This robe has 3 charges, and it regains 1d3 expended charges daily at dawn. While you wear it, you can use an action and expend 1 charge to cause the garment to display a shifting pattern of dazzling hues until the end of your next turn. During this time, the robe sheds bright light in a 30-foot radius and dim light for an additional 30 feet. Creatures that can see you have disadvantage on attack rolls against you. In addition, any creature in the bright light that can see you when the robe's power is activated must succeed on a DC 15 Wisdom saving throw or become stunned until the effect ends.
Notes: Stunned, Control, Debuff, Outerwear
Just think of it as the world's most fabulous flashbang
Would blindsight negate its stun ability?
I think so, if it doesn't have any other mean of sight. A creature aware of the effect should also be able to close its eyes, obtaining the blinded condition.
Nope, it doesn't impose "blinded" condition, just stuns enemies via visuals.
Creatures with blindsight can see without eyes, so it would actually negate it if they're perceiving the user without using their eyes.
Since JC verified a creature is considered to be able to see itself at all times, does that mean the wearer needs to make the save every time as well? The item states all creatures that can see the wearer need to make the save or be stunned, how does that work when the wearer is also a creature that can see the aforementioned "you", which is itself?
Since the description says, "ANY creature in the bright light (30 ft radius) that see you when..." does that mean it affects allies too?
RAW, yes that is what the wording means.
Can affected allies do anything to negate its affects?
Can allies avoid being affected?
They can look away if they know it's coming, but otherwise I would rule that they have to make the save just like anyone else. It's essentially a flashbang in a coat.
“How I love my coat of many colours🎼
Such a Dazzling coat of many colours!”
FROM 1e DMG :: Robe of Scintillating Colors: You need an Int 15 and Wis 13 to be able to use this robe, which will reward the clever with an array of hypnotic colors. Anyone within a 20’ radius must save vs. magic or be transfixed for d4+1 rounds, and when that’s over they need to save again to attack the wearer. Also, each round the robe is flowing, attacks (missile and hand to hand) are made at -1, to a maximum of -5. After the first round, as long as the wearer doesn’t move more than 1”, they can act normally, e.g., cast spells.
Would this still impose disadvantage on a creature with true sight? For example a pit fiend.
So the dodge action with the potential to stun enemies, with the risk that allies would also be susceptible... Very rare seems a bit much.