Stacking Blur and Mirror Image

[phindar]

For example, adding Displacement to Mirror Image is huge.

But its really not. Assuming 5-6 images are created in the casting of the spell, Blur will save one of them, and Displacement will save 2-3 of them. In either case, the caster would be better off casting Mirror Image and then casting it again when it starts to run low. Using a 3rd level slot for Displacement comes close (because of the 2-3 images that will likely be saved, 1-2 might survive again), but thats still a 2nd and a 3rd level spell to get something about as effective as casting the 2nd level spell (MI) twice.

And, none of it helps the images against the stuff that ignores MI, like AoE attacks and creatures with blindsight (like grimlocks, which are not of an ungodly CR). Even the Blind-Fighting feat goes along way towards nerfing MI, and that's a pretty common feat.

While we're beefing (nicely) about MI, are there any higher level versions buried in splatbooks or supplements? What level would you put a version that creates multiple images that work like Major Illusions? Or one where the images didn't disappear when struck?

 

[KarinsDad]

But its really not. Assuming 5-6 images are created in the casting of the spell, Blur will save one of them, and Displacement will save 2-3 of them. In either case, the caster would be better off casting Mirror Image and then casting it again when it starts to run low. Using a 3rd level slot for Displacement comes close (because of the 2-3 images that will likely be saved, 1-2 might survive again), but thats still a 2nd and a 3rd level spell to get something about as effective as casting the 2nd level spell (MI) twice.

Interesting analysis. Flawed, but interesting.

The point you dropped on the floor is that with my interpretation, Mirror Image gives 5-6 images and Displacement merely protects the caster.

Cost: 1 2nd level spell + 1 3rd level spell.
Gain: 1 2nd level spell + 1 3rd level spell.


With the opposing interpretation, Displacement changes the Mirror Image into the equivalent of an Empowered Mirror Image.

Cost: 1 2nd level spell + 1 3rd level spell.
Gain: 1 4th level spell + 1 3rd level spell.


With regard to the rest of what you wrote, the caster is not better off with two Mirror Image spells (as you claimed) since they are totally ablative whereas a Mirror Image combined with Displacement is only partially ablative. The gain is not about as effective (or better off, you claimed both) as 2 2nd level spells as you claimed, rather it is a gain of a 3rd level spell (Displacement) and the equivalent of a 4th level spell (Empowered Mirror Image or a Mirror Image with 7 to 9 images) with this interpretation.


Having the Displacement and MI up is a larger protection versus the back to back Mirror Images that you proposed. The chances to get targeted (let alone hit) as images get popped drops by:

MI (6 images followed by casting 6 images again when down to 1 image) = 16.7% / 20% / 25% / 33.3% / 50% / 16.7% / 20% / 25% / 33.3% / 50% / 100% / 100%, etc. (average 40.8% of getting targeted after 12 successful attacks)

versus

Disp followed by casting MI (6 images) = 50% / 8.3% / 10% / 12.5% / 16.7% / 25% / 50% / 50% / 50% / 50% / 50% / 50%, etc. (average 35.2% of getting targeted after 12 successful attacks)

Most of the time (except for a few successful attacks after casting a second MI), it is better to have up a MI and a Displacement (using my interpretation) than it is casting a second MI. At higher level with opponents having more attacks per round, the dual MI spells come down fast whereas the Displacement lasts much longer (shy of a Dispel).


The other interpretation yields (assuming alternating attacks miss the images due to the combined displacement with the images of that interpretation):

Disp followed by casting MI (6 images) = 50% / 8.3% / 10% / 10% / 12.5% / 12.5% / 16.7% / 16.7% / 25% / 25% / 50% / 50%, etc. (average 23.9% of getting targeted after 12 would have been successful if it did not run into displacement attacks)

As can be seen, this is much stronger than my interpretation where Displacement does not affect Mirror Image (as I originally claimed and you claimed it was not much stronger).

If an opponent Fighter type averages 20 points of damage (combining both to hit and damage), your two MI solution would have the caster taking 98 points of damage, my interpretation with Displacement and MI would have the caster taking 84.5 points of damage, and the alternative interpretation with Displacement and MI would have the caster taking 57.4 points of damage.

So yes, that interpretation of Displacement combining with Mirror Image would be 1.7 times as effective at stopping damage than using two Mirror Image spells. You claimed using Mirror Image would be more effective (or about as effective, you claimed both of these). It's actually much worse off in the long run, espeically at higher levels where opponents get more attacks per round.

 

[phindar]

Well, its an interesting point. I'll note that I responded to your post while you were editing it to clarify. While I take your point that Displacement + MI is more effective, that's one of the things I like about it. Not the power issue-- since it still doesn't seem unbalancing to me-- but I like spells (or effects, or feats) that combine in interesting ways. It rewards the players that try to use their resources as creatively as possible (at least until we all get so jaded that we know all the tricks, and move on to another system with yet more rules to exploit and bend to our will).

I wouldn't say that MI + Displacement is equal to Emp MI + Displacement, becuase of the Durations. While the MI + Blur combo would go for 1/min per level for each, Blur is still probably only going to save one image. Displacement will save more, but Displacement is only one round per level. So its not quite the same as the Empowered MI, because you're only getting it for 1/10th the time.

My perspective on this is influenced by my group tending to concentrate on mid-level play; I suppose if I was running or playing 20th level casters I'd be more worried (but then, at that level, it seems like it'd be pretty easy to use creatures that Mirror Image couldn't really slow down).

 

[John Cox2]

So I've seen a lot of talk on the logic of Blur/Mirror Image stacking, both for and against. I think by reason it could go either way. Wizards prefers the "do stack" rational. And I think there is a very good mechanical reason for that:
Let's say I'm attacking a blurred/mirror imaged creature. If they don't stack I first have to ask for them to make a mirror image roll, then I can attack knowing if it's the image or the character I'm attacking. Roll normal for image and disadvantaged for character. And then I see if I hit.
With stacking, I attack with disadvantage, if my final roll was good enough to hit an illusion then the character makes the mirror image roll. If not no roll is necessary.
The stacking method both expedites gameplay and increases immersion. I as an attacker never know if I was attacking an illusion or not until I hit one.

Edit: Just noticed the post dates on this thread. This conversation was pre-5th edition and my comment was not relevant. I'll leave it though for people like me looking to see if mirror Image and Blur stack in 5th edition.