Does the Legion of Sentinels illusion spell work on Oozes?

Question

I recently had players fight a Brown Pudding in my game, then the Thief/Beguiler of the group casted a Illusion spell called Legion of Sentinels (PHB2 p. 116). A headbutting ensued with him about the Ooze's Mindless and Blind traits.

An ooze possesses the following traits (unless otherwise noted in a creature’s entry).

Mindless: No Intelligence score, and immunity to all mind-affecting effects (charms, compulsions, phantasms, patterns, and morale effects).

Blind (but have the blindsight special quality), with immunity to gaze attacks, visual effects, illusions, and other attack forms that rely on sight. Immunity to poison, sleep effects, paralysis, polymorph, and stunning.

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Does Legion of Sentinels spell works on Oozes?

Answer 1

Ben’s answer is quite good, and the bottom line, that slashing damage isn’t going to work on brown puddings, is spot-on.

He is also completely correct about mindlessness not being a defense here. Mindlessness only protects against spells that try to get into your head (with the mind-affecting tag). Most illusions don’t; most illusions actually produce a real, physical effect, whether that be light or sounds or whatever else. A mindless creature will experience those lights or sounds exactly the same way it experiences the lights or sounds of real objects, and being mindless is probably even more susceptible to being fooled since they cannot reason that something cannot be real.

But what I really wanted to address is blind-but-blindsight. Illusion spells can create sounds, vibrations (which are just sounds by another name anyway), smells, and so on. Which means it is entirely plausible for “a nonvisual sense (or a combination of such senses) [used] to operate effectively without vision” to be fooled by an Illusion spell.

Moreover, Illusion (Shadow) spells are partially real, created out of the shadow-stuff of the Shadow Plane. It’s no different from wall of stone conjuring stone out of the Plane of Earth, only it gets classified as part of the Illusion school instead of the Conjuration school because... it does. That classification makes sense to arcane scholars in the world; maybe the Plane of Shadow has some connection to illusory magics, maybe it just happens to be taught as part of the standard illusion curriculum rather than a standard conjuration curriculum. We don’t know, and it doesn’t really matter to us. The point is, despite being an Illusion, Shadow spells are at least in part real.

Which means whatever “nonvisual sense (or a combination of senses)” the ooze is using, it’s still going to detect the legion of sentinels because the legionnaires are, in fact, actually there to detect. They have volume and probably even mass, there are firm boundaries between the sentinel and the air they exist in, and they produce vibrations and possibly even scents.

In short, an Illusion (Shadow) spell should affect blind-but-blindsight creatures.

That doesn’t change the fact that the sentinels do slashing damage, which isn’t useful here anyway.

Answer 2

Having looked up that spell it's pretty vague and I can completely see why it might be brought up, but I'd rule that it does.

Nothing about the spell is mind-affecting or has any sort of saving throw or spell resistance, so we can ignore Mindless.

Since the spell has the shadow tag, the damage it causes is 'real' in that it can affect physical objects (indeed, it's physical slashing damage affected as usual by damage reduction), and I read the text in Blind as applying to the illusory effects of an illusion spell. Legion of Sentinels is an Illusion school spell but the damage it causes is not illusory and does not rely on sight. Consider what you'd do if someone cast a Shadow-Conjuration Fireball on them - even objects take 20% damage from that, so likewise, so would illusion-immune creatures. For whatever weird reason, Legion of Sentinels does not have this 20% rule and in fact is dealing full non-illusory damage with no resistance or will save or anything, which is odd, but in my opinion reasonably clear from the damage type and text.

On the other hand, black puddings and ochre jellies are explicitly immune to slashing damage - I can't find 3.5e statistics for brown puddings, but in pathfinder they Split against slashing damage. The sentinels would still use up their AoOs against them and rapidly split them into a truly ridiculous number of very low hp puddings... this may be good or bad, since 1hp puddings could be killed by the sentinels in this case, but there'd be so many of them some would possibly spill over, but that's beyond the scope of the question I think?

(The source of what type of damage the spell causes is the PHB2 Errata, as it's apparently missing in the original text)

Edit: According to some sources, brown puddings in 3.5e are simply black puddings that live in marshes. If that's so, then brown puddings would be entirely immune to this spell as it deals only slashing damage, but not because of their Blind tag.