Excelsior

Sometimes when i wander around dungeons, mostly Destard or Blood players that come by have a char model that looks like a see through robe or something. And no, i don't mean the dead char model ^^

What exactly is it that does change your appearance to that.

I hope somebody knows what i mean

Sounds like they are items dyed by the Ethereal Dye Tub. This dye tub is generally avaliable at Auctions. I think they go for around 7 mil, but I may be off by a couple Mil, point is they are not cheap, and they only have 1 use.

Also, there is wraith form spell and medallion of the undead, which both turn you into a semi-transaprent ghostly figure.