Jack Haggerty said:
I have, and I didn't see any problems... Assuming the DM makes it clear that the images cannot flank.
When I've run the mirror images as having their own squares, we ran into some problems (other than flanking). An evil necromancer had cast mirror image. The heroic fighter could 5ft step to one of them, but not the rest.
So the fighter takes his 5ft step next to the one he can reach and rolls to hit. He does, and the DM rolls and that turns out to be the real necromancer. But the necromancy had moved and cast mirror image on his last turn, and he did it 20 feet away from that image the fighter just hit. How did the real necro get over there?
What if the fighter strikes at the necromancer and manges to connect with the real one. Then the rogue attacks an image 20 ft away. Do you roll to see if that is the real necromancer too? Or once someone hits the real one, does everyone else automatically know which one is real?
On the necromacer's turn, he can shift the images around, but what if he prepares and drinks a potion that turn too? Then he can only move 5ft, so you know he has to be one of the images within 5ft of the one the fighter hit last turn.
What if you have three images strung out in a line and the image in the middle gets destroyed? Now one of the images is not within 5ft of another. Does it go away too or does it continue to exist in violation of the spell description?
How many attacks did he get against the necro? Some of the images were behind cover (or completely out of sight behind a wall). What AC is the hero aiming for now? You have to roll to see if it is real or not before he swings.
What if there is a necro and one image and one of them is behind 90% cover. The players have a better chance of attacking the one in the open and hoping for the 50% chance of it being real. Doesn't that seem kind of wonky? Wouldn't the necromancer rather be behind the cover? This sort fo thing really forces the Dm to keep track of where the "real" necromancer is (so that he can use cover, move legally, etc. etc.). But you can bet the players will be able to track the real one too, just through metagame knowlege about 5ft steps and so on. That puts them into the position of having to "play dumb" in a life-n-death situation just because of your rules interpretation. Not good.
How to you even place the images, or control where they move? The spell description does not allow consious control of the images. They "mirror" the caster, "mimic the character's actions", "stay near the character", and "separate from the character and remain in a cluster". They do not obey mental commands or independently react to the evnironment.
Keep all of the images in a cluster (like the spell says) around the caster and you will avoid these problems. At the very least, keep them (and the caster) all within a set of 3x3 squares.
I've played it both ways and there's no way I'd go back to putting images in their own squares. After this much discussion, I'm convinced that others are equally inflexible so I'm more or less done. I just hope that others reading this thread will consider both options and make the right decision.