Can hide in plain sight, melee, spring attack, hide work together?

Question

My character has recently obtained the ability to hide in plain sight. And I am having trouble understanding how it all works. So if my character is hiding (using the hide in plain sight ability). And then moves, performs a melee attack on a foe, and then moves away to hide in plain sight again, does it work?

My understanding is:

Hide in plain sight is a supernatural ability, and therefore it takes no action : see Do special abilities require an action every round they are active?

Spring attack allows me to move, then attack, and then move.

The hide skill ability can be a part of a move action :

Usually none. Normally, you make a Hide check as part of movement, so it doesn’t take a separate action. However, hiding immediately after a ranged attack (see Sniping, above) is a move action.

Is the above all possible?

My other question is, while my character is moving and attacking, is he still hidden, or is he only hidden after the move is completed?

Will the foe know which square my character ended in?

Answer 1

It’s practically impossible (-20 penalty) to hide while attacking, running or charging.

So you can remain hidden while making a spring attack, but the DC to spot you is not going to be very high. If you still manage to win the opposed roll, your target will be denied its Dexterity bonus to AC and will have an additional -2 penalty because you are effectively invisible.

From Skip Williams' column:

If a foe you cannot see hits you with a melee attack and is adjacent to you at the time, you know the foe's location. For this reason, smart foes move right after they attack; even a foe that has made a full attack can move after attacking by taking 5-foot step (provided it has not already moved during its turn).

When an unseen foe hits you with a melee attack from more than 5 feet away, you know the general direction from which the attack came and that the attack came from more than 5 feet away, but you do not know the attacker's location.

That is the main reason to spring attack: you need to move after attacking, even if invisible, otherwise your target will know your location. If your target has failed its spot check, you still have total concealment (50% miss chance).

Answer 2

Yes.

• On your character's turn, you may move, either to close to melee attack or move to make ranged attack and make (another) opposed hide/spot check. If you move more than 1/2 speed, take -5, or -20 if charging (if you charge, you can't use Spring Attack or Shot on the Run). Even without HiPS, you could Sneak Up From Hiding, incurring a -5 penalty per 5' moved from cover/concealment (in addition to movement penalties). If you do not need to move to attack, and you have already succeeded on a hide/spot check, another is not necessary (yet).
• Resolve the attack as a standard action. As long as hide/spot is successful, your opponent is denied Dex bonus to AC and you get +2 to melee/ranged. Or, if you have initiative and your opponent has not acted, even if you lose hide/spot, your opponent is still denied Dex bonus to AC. If this is a character with sneak attack, even if you lose hide/spot and your opponent has acted, you can still gain a melee sneak attack by flanking.
• At this point, if have already taken a move action, you must move using the Spring Attack Feat or Shot on the Run (for ranged) and in any case, make a Hide check (using HiPS) if you want to hide again (or continue hiding) but you incur the -20 penalty for attacking (-5 may also apply, but you can't run or charge at this point). If you don't move after attacking and your hide/spot check was successful, your opponent knows what square you are in, but suffers a 50% miss chance. If you move and your hide/spot is successful, then your opponent must guess at the square and if the guess was correct, still incurs the 50% miss chance.

If you lose the first hide/spot, you don't get +2 to attack and opponent is not (if not otherwise) denied Dex bonus to AC (which may affect sneak attack). If you lose the second hide/spot, your opponent can target you as normal. If both hide checks were successful, you were never seen. If at any point you are seen, you cannot hide without HiPS (as you cannot hide if someone is observing you), without moving somewhere you cannot be observed.

For completeness, Sniping

• On your character's turn, if you were hidden to begin with, at least 10' from your target, you can make a ranged attack with a +2 bonus to attack and the target is denied it's Dex bonus to AC.

• As a move equivalent action, make a hide check at -20 to remain hidden.

Because you need cover or concealment to hide (normally) and you don't benefit from sneak attacks if the target has cover or concealment relative to you, sniping must be done from the edge of cover, meaning no squares of cover or concealment may be between you and the target and you must be in a square of concealment or cover.

Hide In Plain Sight would allow you to Snipe without cover or concealment and without Shot on the Run. SotR would still be beneficial though, giving you an extra chance to hide if seen.

Answer 3

My read (and this would be based on the rules for the invisibility spell):

• You are waiting your turn hiding. Status: Hidden
• You move to the target. Status: Hidden, but I'd give the target a roll to see someone sneaking up on him (if coming from the front)
• You get all stabby with your knife. Status: NOT Hidden.
• You move away using Spring Attack. Status: Not Hidden.
• You get to your safe place and hide. Status: Hidden
• You repeat this process. Status: Hidden as above, but you don't get the back-stab bonus.

I'd take away the bonus because he knows you are back there, but is more worried about the fighter cutting him into ribbons if he turns around to look at you, but his mind is also trying to find spots that he can defend from both attack vectors. I am away from my books so I don't know if there is an "attacking from cover" or similar bonus, but I'd give that (or half of that) due to you being hidden, but known to the target.