Need help with a cosmetic
It sounds like a rendering or loading error. There are options to reduce other player renderings; certainly one of them turns everyone into a pink-garbed avatar, and I think the lowest settings will do that grey effect. Weapons and backpacks are not affected, per many complaints from those who don’t want to see the wings many players enjoy wearing.
So likely you saw someone your game hadn’t fully loaded.
https://wiki.guildwars2.com/wiki/Ghostly_Infusion_
https://wiki.guildwars2.com/wiki/Poly-luminescent_Undulating_Refractor_
Either of these look familiar?
Assuming it was a revenant. :-)
There is a Graphical glitch you can provoke by using the Backwards Dodgeroll utility skill from Shiro and swapping your weapon set on the same frame. It causes the grey mist Animation to infinitely loop on your character.
It causes absolutely no harm and proviedes no benefit other than this unique effect. It gets extra hilarious if you have a way of putting on a costume because some costumes have effects on them that mess with the grey mist texture causing even more graphical confusion.
He glitch ends when you use the Dodgeroll skill again.
It might be this as well: https://wiki.guildwars2.com/wiki/Strawberry_Ghost
Was he near box of fun?