Liked the article.
I think the DMG should add more clarifications. For example, cover and concealment usually both allow to hide, but they are very different things, e.g.:
- a thick glass pane covers you but doesn't hide you
- a thin opaque curtain hides you but doesn't cover you
Being visible is a different thing than being located by someone: the invisible monster/character can be located (i.e. they know there it is) for instance if it's standing into water or sand, of if it's moving, or if it just turned invisible a moment ago. In some corner case (Mirror Image, displacer beasts) someone can even be visible but its true location unknown.
I think 3e had somewhat clearer description for hiding:
" You need cover or concealment in order to attempt a Hide check. Total cover or total concealment usually (but not always; see Special, below) obviates the need for a Hide check, since nothing can see you anyway.
If people are observing you, even casually, you can’t hide. You can run around a corner or behind cover so that you’re out of sight and then hide, but the others then know at least where you went.
If your observers are momentarily distracted (such as by a Bluff check; see below), though, you can attempt to hide. While the others turn their attention from you, you can attempt a Hide check if you can get to a hiding place of some kind. (As a general guideline, the hiding place has to be within 1 foot per rank you have in Hide.) This check, however, is made at a -10 penalty because you have to move fast.
Sniping
If you’ve already successfully hidden at least 10 feet from your target, you can make one ranged attack, then immediately hide again. You take a -20 penalty on your Hide check to conceal yourself after the shot. "
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Generally I have problems with invisible stuff or similarly with blinded characters.
Say you're in total darkness, and you are attacked by someone with darkvision. Probably the attacker still needs a Hide check, because that includes not making noises. But if your Perception wins, you know where it is but you still can't see it! Can we say it's not technically hidden anymore?
But even if it's not hidden, at best you know where it is... but how can you defend normally (dodge, parry) from its attacks, since you don't see the attacks? Shouldn't it still have advantage to attack you?
The attacker would still have advantage on attacks against you since you can't see it. Being unseen and hidden are two different things and you only need to be unseen to get advantage on attacks.