I've been writing my own game for a while and I've been pondering how to do stealth rules. I came up with the following, and I wonder how well it could be implemented in Pathfinder. Let me know if you see anything wrong with it!
Stealth
When a creature does not have line of sight to you or is unaware of you, you are hidden with regards to that creature. If, during your turn, you move into line of sight of a creature you are hidden from, you may roll Stealth opposed by the creature's Perception.
If your Stealth roll is less than the creature's Perception roll, it spots you attempting to sneak out of hiding. You may complete your movement but the creature is aware of you and can react accordingly (if able).
If your Stealth roll equals the creature's Perception roll, you manage to stop yourself before being spotted. You can continue to move, but are automatically spotted if you do (as above).
If your Stealth roll exceeds the creature's Perception roll, you remain hidden while moving for a distance up to 5 feet plus an additional 5 feet for every 5 points by which your roll was higher. If you are still in clear (no concealment or cover) line of sight when you move beyond the end of this distance, you are spotted. If you have not exceeded this distance by the end of your turn, you are still hidden until you take an action that would reveal you or you end your turn. If have not exceeded this distance by the time you reach a position with concealment or cover with regards to the creature, you remain hidden from it.
Example 1:
Alice is hiding in a bush 20 ft. from Bob. She wants to sneak up on him!
Alice rolls Stealth: 20!
Bob rolls Perception: 25!
Result: Bob spots Alice rustling in the bushes.
Example 2:
Scenario as above.
Alice rolls Stealth: 20!
Bob rolls Perception: 20!
Result: Alice goes to move but sees Bob looking her way. She can decide whether to come out in full view of him or not move and remain hidden.
Example 3:
Scenario as above.
Alice rolls Stealth: 25!
Bob rolls Perception: 20!
Result: Alice can get 10 feet from the bush without Bob noticing. If there is another bush in that distance, she can hide in it and remain hidden. Otherwise, at the end of her turn he will notice her if she moves out.
Example 4:
Scenario as above.
Alice rolls Stealth: 30!
Bob rolls Perception: 15!
Result: Alice sneaks up the full 20 feet between the bush and Bob. Since she has not exceeded her stealth distance so she is still hidden until she ends her turn. She uses her remaining action to tickle Bob with full sneak attack!
moving for a distance up to 5 feet plus an additional 5 feet for every 5 points by which your roll was higher.
Add the line "up to your total movement", to prevent players thinking they can get extra movement from really high stealth rolls.
My thoughts:
1) This could become overly complicated when sneaking near lots of creatures.
2) It seems a little bit like metagaming to me, as a sneaking character does not necessarily know if they have been spotted or not, ie, what the opposing perception roll is, and rather or not coming out of cover is a good or bad idea. Perhaps a perception check from the sneaking character would fix that, but add even more complication.
That being said, if you don't mind the extra book keeping it sounds fine if you're into that kind of thing.
The thought was that the GM would roll Perception secretly and alert the player if relevant. The player gets to decide how far they want to risk moving before knowing the result. I suppose that's a bit unclear there.
As for multiple characters, their Perception checks would simply determine the order in which they spot the sneaking character, if they are successful.
I thought about opposed Perception checks in that instance, but dropped it for the reason you mentioned: Complexity. It is meant to represent that recognisable one moment one sees in stories and films: Where the hero goes to move around a corner and ducks back just moments before a guard turns to look. Naturally, this only applies if the sneaking character is already aware of the observer.
Addendum: The slightly awkward mechanism for feet per 5 points of success is an attempt to squeeze the mechanic into a 5 ft. square system. The original uses 1 metre as the minimum measure, and allows stealthy movement of 1m per 1 point of success (non d20, so the potential range is smaller).
I think I'll take another attempt at this soon, with clearer explanations (and maybe diagrams). Anyone interested?
When a creature does not have line of sight to you or is unaware of you, you are hidden with regards to that creature. If, during your turn, you move into line of sight of a creature you are hidden from, you may roll Stealth opposed by the creature's Perception.
emphasis mine
You are using the word hidden as if it were a condition which, AFAIK, doesn't exist in Pathfinder. Hidden as a condition needs to be defined.
Oh well. I suppose that achieves the same thing as my rule, but has no distance limit.