Ilbranteloth
Explorer
If I duck behind a hedgerow or low wall, and you know that I'm there because you saw me duck, am I hidden? If I duck behind a lone tree, and you know that I'm there because you saw me duck, am I hidden?
Do you know for sure that I didn't climb up the tree or crawl to one side of the hedgerow? Do you know for sure that I didn't stealthily walk away? How many times can I successfully pull off the trick of making you think I'm somewhere else before you finally catch on that I'm staying in the same spot?
Hmmm...
If you succeed in your Hide check countered by the opponent's Perception, yes. If not, no. The question is how easy it is for you to hide, and that's very circumstantial.
That's why I said that it MAY be at a disadvantage.
There's been a lot of discussion about whether you're actually there, whether I actually know, etc. That's part of the purpose of the Hide check. You've run behind something that obscures you, then make a Hide check to see if I know where you are or not. Or whether I think you're someplace else.
If you succeed, then when you pop out from behind the tree to attack me, I'm not expecting it and you have advantage.
If you fail, then I'm expecting you to be there, and to attack me from there. I'm paying closer attention so when you pop out I see you, so you are no longer hidden, and don't have advantage attacking me.
While the rules state that Hidden = not seen and not heard, they also allow a Perception check to foil your attempt to Hide, even if you are not seen and not heard. Some creatures have abilities that give them advantage on Perception checks because of other senses, like smell. You may fail your Hide check because of that as well.
I'm just saying that in certain circumstances, it's harder to fool the opponent, and thus you have disadvantage on your check. If you've ducked behind the same wall 3 times, and come out and attacked from the same place, then I'd rule you have disadvantage the next time you try it. But if you try to Hide and move to a new location you wouldn't have disadvantage because it's not what the target is expecting.
If you duck behind a low wall, and make sure that your sword sticks up a little above the wall, and you prop it up and leave it there and sneak further along the wall, I would say you have advantage on your Hide check because you've given me a creative way to try to fool the opponent, regardless of the fact that he just watched you go behind the wall.
Mike Mearl's response was to the question of whether the halfling could use the same hiding trick over and over. He said yes, but that it would probably be at disadvantage.
The answer uses a core mechanic, and was actually already in the rules: The DM can also decide that circumstances influence a roll in one direction or the other and grand advantage or impose disadvantage as a result. (pg 57).
Randy