I was knocked unconscious (hit a 16 while I had 16hp left, naturally) with one clone from mirror image still active. The spell isn’t a concentration, simply a duration of one minute (it had only been maybe 5/6 rounds of combat at that point.

And then the dm decided to be brutal and attack me twice more rather than switching targets, meaning two auto crits and an instant death for me. Would my mirror image at least have a chance at taking one of those two hits if I rolled the required 11?

My dm said no, because I’m not moving and the creature wouldn’t have any difficulty discerning which one was real at that point. But isn’t that the idea? It’s a strong illusion magic, shouldn’t it still be able distort a still object?

There’s nothing in the spell description indicating it would become inactive just because you’re incapacitated. Any ideas on how this plays out?

As you point out, there's nothing in the spell description that states the effect ends if you're incapacitated. It ends when the last duplicate is destroyed or when the duration expires.

Your DM is welcome to do whatever they want at the table, but this decision was not RAW, and ad libbing a house rule specifically to kill a PC feels like a breach of trust to me.

According to the rules, your DM is a jerk. Leave that game.

The spell relies on sight, but the only provision given in it says that creatures with blindsight and truesight are unaffected. If the NPC was in fact basing his judgement on sight then by definition, he is still affected. The mirror images mirror you (hence the name) so if you're not moving neither are they.

Incapacitated means you cannot move or take actions, that is all. Auto-crits are not a part of that condition (unless you mean that you were actually unconscious). But even then, it sound like your DM is out for blood and not fun. Why not play to have fun?

Unconscious, that’s what I meant, brought down to 0hp. But yea, after seeing my dm give so much leniency to everyone else in my party (extra rolls to see if a creature switches targets after they get knocked unconscious, or giving them advantage on death saving throws) I do feel cheated.

Especially now that I know I should have survived at least another round by the rules alone (assuming I rolled an 11+ with one of two d20’s)

The spell says: "Three illusory duplicates of yourself appear in your space. Until the spell ends, the duplicates move with you and mimic your actions, shifting position so it's impossible to track which image is real. "

So as you went down to the floor you were moving and so were the illusions which shifted position with you. So, no, the attacker would have no way of knowing which one was real unless they were immune to illusions or had something like true sight or blindsight.

I agree with the others. Your DM cheated you.

Thanks for the responses guys. Good to know I’m not overreacting