A shadowdancer can use the Hide skill even while being observed. As long as she is within 10 feet of some sort of shadow, a shadowdancer can hide herself from view in the open without anything to actually hide behind. She cannot, however, hide in her own shadow.
Do I need to hide in a larger creature's shadow, or does any shadow work?
Nowhere in the rules is it specified that I've found. That would be too easy. :)
At first glance you would think that it needs to be a shadow large enough to hide in, but note that the rule says you need to be within 10 feet of a shadow (rather than in one). Also note that you don't have to move to make a Hide check (although you often are moving while hiding).
That means it's entirely within the rules to stand still, with a shadow two squares away that you can't reach, and use it to hide with Hide in Plain Sight. The implication from that is that the size of the shadow doesn't actually matter as you're not actually trying to fit in it.
In the game I'm DMing, I wouldn't allow miniscule shadows because they'd lead to arguing ridiculous things like that a copper coin laying on the ground creates a barely visible shadow and thus you can hide anywhere, but I do allow a shadow for any object of any significant size that's got a light source behind it. Things like other characters, doors, barrels, chairs, and so on. Essentially, anything that's a small size object (or larger) that is casting a shadow.
In a dungeon, if the second player in a line has a light source, the Shadowdancer could pretty easily be scouting ahead, as the first player is going to cast a lengthy shadow. If two people have light sources and the Shadowdancer is between them, it can get confusing.
Rules as written, you just need a shadow, absolutely no if-and-or-but about it. That means if there’s a blade of grass, a grain of sand, then there is a shadow, and you can hide in plain sight. Unless it’s literally a featureless plane with absolutely nothing to block the light, the ability works as written. Even deep underground in pitch blackness, no light to cause shadows, you still count because if nothing else, the hundreds of miles of earth and stone is casting a “shadow” from the sun to cause that pitch blackness.
Which leaves only a featureless plane, a plane where light literally does not exist, or a plane where light is literally everywhere from every angle and shadows are impossible.
But one can stipulate that the authors wouldn’t have bothered to say “within 10 feet of some sort of shadow” if they meant that to mean “pretty much always, for all intents and purposes.”
The problem is that, since we’re pretty sure the rules as written aren’t what the author intended, we’re left with vanishingly little idea of what is necessary. The pitch-black area of no-light-at-all probably should deactivate the ability. Blades of grass and grains of sand probably aren’t sufficient. But where exactly to draw the line has to be up to the DM.
Personally, I pretty much allow the ability to work pretty much all the time, pretty close to as-written, even though I agree that probably wasn’t intended. That’s because I find skills, and the characters who focus on them, to be too weak, too easily obviated by use of magic. Having your skills actually work for a change is a good thing, in my opinion.
I would interpret the phrase "As long as she is within 10 feet of some sort of shadow" as "As long as she is within 10 feet of an area of Shadowy Illumination or Darkness".
The reason being that "some sort of shadow" is not a defined term, but Shadowy Illumination and Darkness are - I would argue these are the closest equivalent terms. Further, the issue of whether a Shadowdancer can hide is primarily a tactical problem, and light levels are already a factor in tactical combat.
So, the ability could be used in the following manner:
It may not hinge on any clear definition of "shadow", but it is very easily usable and fits within the rule framework.
I would advise Shadowdancers that are worried about this being an overly strict interpretation to make their own Shadowy Illumination. It is generally not difficult.
My own hypothesis on why they used an undefined term is the one of the Shadowdancer having been written before the current illumination rules were, and it never receiving a proper overhaul.
– Ernir Jul 21 '13 at 17:57
