Right now some of my players are chasing an opponent who is trying to escape. The opponent is invisible but they've "tracked" him by doors being open and that kind of thing. Right now they suspect (correctly) that he's in an escape tunnel that's 5 feet wide and maybe 7 feet tall.
...but since he's invisible, they don't know which square he's in. So they want to fire down the corridor (since it's literally a 5 foot wide line) in an attempt to hit the invisible foe.
How would you adjudicate this?
"You miss."
They're using bows, not laser beams. Arrows are affected by gravity. If it's aimed high enough to hit someone standing 20 feet away, it will go over the head of someone 15 feet away, and fall at the feet of someone standing 25 feet away.
An arrow fired horizontally will go quite far before it falls that much. I'd just give them the 50/50 if he's in the first range increment.
Invisibility grants 50% miss chance, so I'd let them make attack rolls without knowing the square in these circumstances with that concealment.
How would you adjudicate this?
I would use the standard rules.
Knowing that "the target is somewhere on this line" already gives the PCs a higher chance of picking the right square than "the target is somewhere on the grid".Your blaster sorcerer should be happy: it is one of the rare situations where his lightning bolt will prove to be useful...
My first thought was to go with Fuzzy-Wuzzy, but really a 5' wide corridor gives a reasonably wide arc to fire along, e.g if they're close by and/or by one side of the corridor then the arrow could easily miss. I also accept that an arrow or crossbow bolt would fly in a fairly straight line if fired for a short range (the first increment as suggested by Fuzzy-Wuzzy seems reasonable) and so there should be some chance of hitting if the arrow or bolt passes through the target's square.
Presumably the players are arguing that they should have the 50% miss chance regardless of square as they are firing down a line.
My recommendation would be to tell the players that by the rules they must pick the target square but you will allow a 75% miss chance if they are firing flat along a line, without picking a specific square but the arrow/bolt is only effective for one range increment.
What chance would you give a character firing at a empty square in front of or behind an invisible creature?
Relevance? They can see the square, so a normal to hit roll. Technically, it could be argued that the square behind has cover from the invisible creature but it is easier to assume the invisible creature is missed.