Stealth in Battle

I'm not sure how to ask this question.

Mechanically, in Ace, I figure stealth could be a buff to TGR. Maybe that buff could depend on the median ACC of all your enemies in an evented skill.

Perhaps having this state could give that actor access to certain skills such as "backstabbing," or "pickpocketing."

What I'm asking here, though are the other applications. How do I make stealth more than just "the actor is not targetable?" How do I squeeze more juice out of stealth in battle?

I figure fear would be a big thing. People fear the most what they can't see. How could the enemy be afraid of the player? How could fearful enemies be implemented into gameplay?

'Stealth' could be a state the character goes into, and if you want to say enable certain skills that way, you can make so that this state 'adds skill' to the character whilst they are in this state. Even better, you could make several stages of this, e.g. - slightly hidden, concealed, ghost, etc. So say at first the character enters the first stage that reduces their TGR slightly and enables 1-2 weaker stealth skills. Then perhaps in this state they are also able to go further via a skill that gets unlocked in this state (maybe to have a warm up period for this so that the player can't go into that too soon), and activating that skill gets the player to go into the second stage with stronger stealth skills and even further reduction to TGR, and so on so forth.

Edit: Higher evasion rates and all those kind of stats can also be applied to stealth, I think. So the character in a stealthy state has a higher chance to dodge enemy attacks.

It depends. In RPG combat, I guess reducing enemy Evasion to 0 against a character that is in stealth could be an interesting factor (you cannot dodge something you don't see). Not exactly 100% accuracy, as you can miss simply by your own failure to execute the move. Alternatively - negates enemy block rate since you cannot block invisible attacks. 

If you can somehow add this into AI - making the enemies wonder around, trying to attack empty spots in order to "guess" where the hiding enemy is would also be an interesting addition. However you would have to make sure you give the player some kind of clue that the enemy is "searching" rather than the AI just bugging out and doing weird stuff. Like in some games, the enemies would say "Where are you? I will find you! Come out, chicken!" and stuff like that to suggest they are aware of enemy around, but they simply have no clue where he is. (Redundancy -> If the enemy just acts randomly when you go to stealth, the player will wonder why the AI is bugging out)

Aside from that - already mentioned TGR decrease, EVA up, extra skills enabled, etc.

Also a great idea. Several different states of concealment - if you have the time to add them - are always a nice touch. 

I thought about buffs that remove TGR which would be situational and environmental; equipping something green will only buff TGR while in the woods, but not the desert. Equipping shiny armor would raise TGR in all environments. I'd have to play around with scripts and events, though.

Perhaps a darker region would give the actor a buff when they enter combat while standing on that tile.

As for the search event, I guess the enemy would enter a state in which they actively search for you. This would probably translate to gameplay as a countdown or a series of variable checks.

There is a skill in Etrian Odyssey IV for the Nightseeker class called Shadow Cloak, this ability Nulls one physical attack in the next 3 turns, it's a different way to work the stealth mechanic, it offers the enemy a way to break through it if they attack the character 2+ times in one turn which is great for balance and strategy, there is also another passive skill in the game called Auto-Cloak which gives a chance to give Shadow Cloak at the beginning of each battle. I love this mechanic and it gives the player that Assassin-ish feel very well while not being OP.