This question was inspired by a comment on this question.
Normally when a 'thing' (Usually creature, but type in my games doesn't always mean as much as it should by RAW) turns invisible anyone around knows its location (Or square, given a grid system) due to noise, prints, smell etc. I have never been satisfied with this but the comment that inspired this question states:
The DM could decide you are automatically Hidden when unseen, but
shouldn't, as it is horribly unbalanced
And I am not 100% sure that is true.
Assumptions I am going to make:
- Going invisible makes you hidden immediately and automatically (No action needed and no DC to detect, just straight hidden unless something can see invisible things or has another means such as tremorsense)
- Anyone moving normally while invisible (IE: Not in the middle of other actions) is going to be quiet generally because it defeats the point of going invisible then shouting and stomping around
- Attacking, talking, casting a spell, running (IE: the dash action) etc will still give away location
- Once the location is known then re-hiding is not automatic
Assuming the above what are the balance effects of making hidden the default state for invisible creatures?
Best Answer
Turning Invisible should not make a character automatically Hidden
There's a couple reasons why.
What did they roll for Stealth?
If a character is "automatically hidden", then as DM, you need to come up with a way to adjudicate any potential attempts an opposing character might make to detect their presence. You can't just have them roll a D20, because if they roll poorly, then they'd be automatically detected by the passive perception of their enemies, and wouldn't be "Automatically hidden"; that's a paradox.
And you can't necessarily just take their passive Stealth score either, since that might not be high enough to pass the passive Perception score of their enemy. And if you base it on the perception scores of their enemy, then it becomes a weird mechanical consequence where the better a creature's perception is, the better Invisibility becomes against them, which cannot be right.
It makes Stealth too easy
Assuming you resolve the previous issue, this change also makes invisibility too powerful in a combat scenario.
Under the normal rules:
Conversely, under this rule:
Two of the most critical chances the enemy creatures had to take down the Wizard has been removed. Under the normal rules, an Invisible Wizard can be thwarted by attacks made against them, and a failed Stealth check.
Under your modified rules, neither of those are credible threats. The only thing an enemy creature has is to either succeed at their Perception checks (probably more than once before it works!) or target a random spot and hope they land a hit. That is a very significant increase in power.
"Okay, so what if turning invisible instead means they make an automatic /attempt/ to hide?"
This is a lot less overpowered, but still potentially problematic. It represents a middle ground between the normal rules and the scenario with your rule:
So it's less extreme, but it still means a lowered chance of successfully shutting down the retreating Wizard. In particular, it means that the enemy creatures probably won't get to make any attacks against them, and therefore no attempts to break concentration. That still makes Invisibility a lot more powerful.
This also steps on the toes of the Rogue, especially Arcane Trickster, class
The advantage that Rogues (and certain other classes like Ranger) gain is the ability to, among other things, take the Hide action as a Bonus Action in addition to a regular Action. So if an Arcane Trickster were to cast Invisibility during their turn, they'd then be easily able to Hide afterwards, doing as part of the features granted to them by their class/archetype something that you're now going to give for free to everyone.
Conversely, this could also make Arcane Tricksters very powerful: if they no longer need to use the Hide [Bonus-]Action, then they could do something else, like Dash or do something with their Mage Hand Legerdemain feature. No longer requiring an action to use their Stealth would free up their Action Economy significantly, and for a Rogue, that can be a dangerous thing to do.
Conclusion
The stealth rules are written the way they are for a reason, and if you're planning to change those rules, you need to have a clear conception of why you're changing them and what the consequences of that change will be. The rules for Hiding (PHB, pg. 177) specifically call out Invisibility as a condition under which hiding is "always allowed", which implies as a consequence that being Invisible does not make a creature automatically hidden:
So in general, I would not advise this change. Don't turn Invisibility into an automatic "Get out of Combat Free" card. Specializing in Stealth will already make most Invisibility uses very powerful; it's not necessary to go any further.