I figure this is probably one of those things that just about everyone knows about-- except for me, due to my general lack of interest in these sorts of details. But after what happened today, I find myself curious and interested in learning why.
I was in the Imperial City doing the six daily district jobs, and a funny thing happened while I was doing the one where you're supposed to kill Xivkyns and put charged crystals or gems into skeletons so they can be used as spies. As always, there were plenty of players from the other two alliances running around trying to kill our side and flip the flags, but for a short time our side more or less had the district and were unmolested.
Then I see a player from one of the other two alliances, and she is basically a shadowy ghost, which I thought was just a skin, or outfit style, or set gear, or active skill, or whatever-- I mean, I've seen players running around as all sorts of glowy or ghostly or electrical figures, and I'm pretty sure I'd seen this particular type of shadowy figure before, but hadn't thought anything of it.
However, I noticed that this player wasn't attacking us, but was staying a short distance from us and crouching as though sneaking, except every several seconds she would stand up and raise her staff like she was activating a skill or something-- which is something I've seen certain PvP players doing while they're streaming, except of course in the stream the viewers can see the streamer's character as a shadowy figure because we're seeing their character as they do.
And then I realized that the other members of my alliance apparently couldn't see this enemy player, because they weren't reacting to her presence at all. We killed the Bone Colossus or whatever, so we could implant a gem in the skeleton, then the other players in my alliance moved off-- probably to look for more skeletons to implant-- but that had been my fourth and final skeleton so I stuck around for a moment. The shadowy enemy player crept forward once the other players left, implanted a gem in the skeleton, and snuck away.
So I have two questions: (1) What skill or potion or whatever was she using to make herself invisible? And (2) why was I able to see her even though the other members of my alliance apparently could not? The character I was playing on is a Redguard Nightblade, but I don't think I was wearing any special stealth-detecting gear-- I'll look at it later tonight to check whether it has any special bonuses-- and I wasn't using any Detect potions, or any other potions for that matter.
I've fought mudcrabs more fearsome than me!