sources of losing dex bonus to AC

[King of Nowhere]

i was picturing a scenario in which, during battle, a new opponent reveals himself from hiding and sneak attacks.
then i went to read the exact rules, and it turns out a creature is only considered flat-footed if it hasn't acted in combat yet; so in my scenario it would keep the dex bonus, and it would not be eligible for sneak attack.
i can find some partial support for my interpretation with the "invisible" condition, where the attacker denies dex bonus to the defender. if the attacker was successfully hidden, then it is effectively invisible to the defender, and therefore it can sneak attack - and it also gets an additional +2 to hit. regardless of exact wording, this seems the most sensible interpretation.

this situation hasn't happened at my table yet, but with rogues both in the party and against it, it's only a matter of time before it does, i'd like to check how much my interpretation can be supported under the rules.
also, i wanted to checks other ways to get sneak attack besides flanking and acting first.
thanks

[Biggus]

The Rules Compendium agrees with you (p.92):


If you’re successfully hidden with respect to another creature, that creature is flat-footed with respect to you. That creature treats you as if you were invisible

[Metastachydium]

also, i wanted to checks other ways to get sneak attack besides flanking and acting first.
thanks

Technically there's feinting too. Or you can somehow force the opponent to start climbing or something.
Also, you can sneak attack stunned or helpless opponents.

[TheStranger]

The Rules Compendium agrees with you (p.92):

This is the rule, but your players should probably get to roll spot checks as a hiding enemy moves into position. So unless your whole party fails their spot checks, “sneak attack out of nowhere” might not work as planned.

An actually invisible enemy could pull it off easily, though (assuming none of the PCs have a way too see them). Depending on level and what you want to give for loot, the enemy rogue could use a potion/wand/ring/whatever to be invisible until they attack.

[King of Nowhere]

This is the rule, but your players should probably get to roll spot checks as a hiding enemy moves into position. So unless your whole party fails their spot checks, “sneak attack out of nowhere” might not work as planned.

An actually invisible enemy could pull it off easily, though (assuming none of the PCs have a way too see them). Depending on level and what you want to give for loot, the enemy rogue could use a potion/wand/ring/whatever to be invisible until they attack.

which brings up the question; the party enters a room and commence a fight against some visible enemies, the hidden one breaks cover and attacks. if one or two party members succeed their spot check, but the others don't, those that don't lose dex?
I would rule that those who made the spot check can shout something like "watch over there, there's a hidden one", which would allow those who failed the spot check to make a second check with a +5 circumstance bonus. Unless a party member actively goes to attack the guy, breaking his cover. I would also decide who the rogue attacks before having the party roll spot, the rogue does not know who's seen him and who didn't, it's the best i can do to replicate this lack of knowledge.
but this seem full dm adjudication terrain

[pabelfly]

Here's a quick guide on how to qualify for Sneak Attack:

https://forums.giantitp.com/showthread.php?124251-Monk-Rogue-Multiclass-Good-or-Bad&p=6893722#post6893722

[TheStranger]

which brings up the question; the party enters a room and commence a fight against some visible enemies, the hidden one breaks cover and attacks. if one or two party members succeed their spot check, but the others don't, those that don't lose dex?
I would rule that those who made the spot check can shout something like "watch over there, there's a hidden one", which would allow those who failed the spot check to make a second check with a +5 circumstance bonus. Unless a party member actively goes to attack the guy, breaking his cover. I would also decide who the rogue attacks before having the party roll spot, the rogue does not know who's seen him and who didn't, it's the best i can do to replicate this lack of knowledge.
but this seem full dm adjudication terrain

I was thinking about that as I wrote my earlier post. I agree with the idea of a warning, but I don’t think +5 is enough. That’s not much on an untrained check above low levels, and I don’t like the idea that the fighter should be unable to defend himself against a nonmagically hiding rogue after he knows where to look.

OTOH, hearing a warning, turning around, spotting the threat, and defending appropriately isn’t something that should automatically happen instantly. So maybe a +5 on the immediate reroll but the rest of the party automatically spots the enemy rogue at the start of their next turn (or when he stabs somebody). Sort of like a surprise round in middle of combat, I guess. Yeah, firmly in DM adjudication territory here.

[Biggus]

I was thinking about that as I wrote my earlier post. I agree with the idea of a warning, but I don’t think +5 is enough. That’s not much on an untrained check above low levels, and I don’t like the idea that the fighter should be unable to defend himself against a nonmagically hiding rogue after he knows where to look.

OTOH, hearing a warning, turning around, spotting the threat, and defending appropriately isn’t something that should automatically happen instantly. So maybe a +5 on the immediate reroll but the rest of the party automatically spots the enemy rogue at the start of their next turn (or when he stabs somebody). Sort of like a surprise round in middle of combat, I guess. Yeah, firmly in DM adjudication territory here.

+5 sounds fairly generous to me. The skill trick Point It Out (CSco p.88) does pretty much exactly what you're talking about and only gives a +2 bonus.

[King of Nowhere]

I was thinking about that as I wrote my earlier post. I agree with the idea of a warning, but I don’t think +5 is enough. That’s not much on an untrained check above low levels, and I don’t like the idea that the fighter should be unable to defend himself against a nonmagically hiding rogue after he knows where to look.

OTOH, hearing a warning, turning around, spotting the threat, and defending appropriately isn’t something that should automatically happen instantly


I'm thinking specifically of those pictures where there is a guy in heavy mimetic gear hidden somewhere, and the caption says "find the guy hidden in the picture". If you don't know there's somebody in there, you won't look twice and you're unlikely to see anything. but even knowing there's someone in the picture, you don't always find them immediately. You'll probably need some time, which in d&d would entail rolling a new spot check every round until you score high enough.
You're already engaged in combat, and someone shouts that there's a well-hidden ambusher in more or less a certain direction, and you only have a few seconds to notice before he strikes? You're still likely to be surprised.

I also don't like that high level game devolves into gradually stonger forms of invisibility, countered by gradually stronger individuations. Nor do I like that skill use is gradually made moot by spells that achieve the same effect, or that boosts the skill to a level that even an untrained user will always be successful. My general paradigma for keeping martials relevant is "magic is powerful, but can be countered by other powerful magic. Lack of magic is less flashy, but it's often harder to stop completely". So, I'm all for letting people use to their advantage a high skill modifier.

[Telonius]

I just found this guide (https://forums.giantitp.com/showthread.php?186283-Flat-footing-compendium-(3-5))about how to cause either the flat-footed condition, or cause the target to lose Dex to AC*. Looks pretty comprehensive.

*These two things aren't exactly the same thing - stuff like Iajutsu Focus needs the flat-footed condition specifically - but if we're talking Rogues, either one will do.