1) Armor have no "size" : A Medium character can use an armor he finds on the body of a small character and reverse.
YES/NO
2) In exploration mode, if a Rogue character attempts to be stealthy, but travels with a group that makes light and we're in a dark cavern, the Rogue can't use Stealth for initiative anyways and must roll initiative on Perception.
YES/NO
3) The Rogue should declare than he uses Nimble Dodge before the attack die is rolled.
YES/NO
4) As of today, there is no skill/feat/ability that let you diagnose if a character has a disease or is poisoned (you have to treat those withjout knowing if it is necessary).
YES/NO
5) There is no penalty to attacking when you are prone. And you can do so even if one of your ally for example is in the same square of you and is attacking too. By the Book, you could even be 20 characters on the same squere all attacking the same monster without any penalty to attacks as long as at least 19 of you are prone.
YES/NO
Whatever the "official" answer, we feel that all of the above points may need a bit of clarification in the rules.
1) Armor have no "size" : A Medium character can use an armor he finds on the body of a small character and reverse.
YES/NO
No. Small armour and weapons are different, but only the one statline is mentioned because there are no adjustments required, other than the fact that they can't be used by creatures of the wrong size. See p.191, items and size.
2) In exploration mode, if a Rogue character attempts to be stealthy, but travels with a group that makes light and we're in a dark cavern, the Rogue can't use Stealth for initiative anyways and must roll initiative on Perception.
YES/NO
This one depends on the cavern, tbh. If the rogue can break line of sight and get cover, he can stealth - the party, however, is extremely obvious.
(just because you have light shining on you, doesn't mean you can be seen through a crate or a wall)3) The Rogue should declare than he uses Nimble Dodge before the attack die is rolled.
YES/NO
Yes, because it triggers off being targeted (rather than being hit).
4) As of today, there is no skill/feat/ability that let you diagnose if a character has a disease or is poisoned (you have to treat those withjout knowing if it is necessary).
YES/NO
Huuuh... I... think you might be right? You could indirectly determine poisons/diseases by using Status or similar magic that determines Conditions, but it's clearly not the intended use.
5) There is no penalty to attacking when you are prone. And you can do so even if one of your ally for example is in the same square of you and is attacking too. By the Book, you could even be 20 characters on the same squere all attacking the same monster without any penalty to attacks as long as at least 19 of you are prone.
YES/NO
p.323, Conditions, Prone: You’re lying on the ground. You take a –2 circumstance penalty to attack rolls. (there's more to it but i'll stop at the first line).
This one is extremely clear.Also, reading p.311, you can totally climb atop a prone creature, but whether you're able to climb on top of a pile of creatures or a big creature is up to the GM.
Personally I would avoid being prone like lava. -2 to all attacks, -2 to AC, vulnerable to sneak attacks, I have to use an action to get out of it, and I provoke reactions?
It's over.
They have the high ground.
5) There is no penalty to attacking when you are prone. And you can do so even if one of your ally for example is in the same square of you and is attacking too. By the Book, you could even be 20 characters on the same squere all attacking the same monster without any penalty to attacks as long as at least 19 of you are prone.
YES/NO
p.323, Conditions, Prone: You’re lying on the ground. You take a –2 circumstance penalty to attack rolls. (there's more to it but i'll stop at the first line.
This one is extremely clear.
Also, reading p.311, you can totally climb atop a prone creature, but whether you're able to climb on top of a pile of creatures or a big creature is up to the GM.
Personally I would avoid being prone like lava. -2 to all attacks, -2 to AC, vulnerable to sneak attacks, I have to use an action to get out of it, and I provoke reactions?
It's over.
They have the high ground.
Well, this one occurred as a consequence of my character falling unconscious, then the fighter moving up in my square to continue the fight and protect me, and then the cleric healing us, which got me back into the action.
As we were playing update 1.2, I was slowed 1. So I had 2 actions, and I couldn't crawl away and attack in the same round. Therefore, I decided to cast my Produce Flame cantrip from the prone position between the fighter's legs. Fun times, but a tricky rules question.