IcyCool said:An orc under the effects of Mirror Image just ran into that room. I chase him, but see no-one. Then I get stabbed in the side by an invisible foe. The dastardly orc is now also under the effects of a Greater Invisibility spell! I lash out where I believe him to be.
Edit - He didn't cry out in pain, so I must have hit another one of those blasted images. No problem, I can Cleave! I lash out into another square that I believe him to be in. Not there again! Must have been another image! Good thing I have Great Cleave, I lash out again!
Except that none of what you wrote here works.
1) A Major Image cannot emulate invisibility because it is a visual image of something visible (the point I was making to Hyp).
"This spell creates the visual illusion of an object, creature, or force, as visualized by you."
Note: Force here refers to things like a fire.
2) You cannot Cleave off an image, hence, you cannot Great Cleave off an image.
3) Mirror Images of an invisible caster are not applicable until he becomes visible.
"An attacker must be able to see the images to be fooled. If you are invisible or an attacker shuts his or her eyes, the spell has no effect."
Even in your scenario, the character does not get a second swing at the Orc. He either hits the Orc, or he misses. There are no images to hit (i.e. the spell has no effect).