So, Leomund's Trap, also known as Phantom Trap. I've never looked at this spell before (I think I probably just immediately skipped over it because expensive material components are annoying—sometimes necessary for balance, but annoying), but I kinda wish I had, because it seems hella weird to me. It's one of those game elements that just gets stranger the deeper I look at it.

So it's a 2nd level Illusion spell that's Permanent. Not Permanent until discharged; Permanent. That's a little cool, and it's probably why the expensive material component is there. It also has no saving throw and no SR, so it's hard to straight up ignore it if you're below True Seeing levels. And it's apparently 100% effective; "any character able to detect traps, or who uses any spell or device enabling trap detection, is 100% certain a real trap exists." No check, no save, no nothing: it just works. Which gets even weirder when we consider that anyone with Trapfinding doesn't have to actually be looking for traps; they just look at the enspelled item and immediately say "that's the trappiest trap I've ever seen in my life."

That's sort of interesting, now that we look at it, don't you think? It doesn't specify in any way what the onlooker thinks such a trap might be, of course. The text is entirely silent on that. Nor does the text specify that there's any way of disabling said "trap", unless it falls under the general-purpose Disable Device rules for "magic traps," which the spell kinda is and kinda isn't. I feel like it isn't, really, but if it's true that it isn't, then a Rogue (or whomever) who tries to disable the "trap" will always think they failed. Always. Because the trap is still there. And they know this with absolute certainty. No save.

Even if they decide to open the enspelled item anyway and see that nothing happens, they still think a trap is there. With 100% certainty. The spell doesn't discharge. It's still there, and therefore it's very clearly still trapped, as anyone (with Trapfinding) can tell. Even the text (indirectly) states this: "nothing happens is the trap is 'sprung,'" and the onlooker realizing that the item isn't trapped would probably qualify as something happening. The spell does not change.

In fact, since there isn't a "disbelief" clause (and therefore the "you automatically disbelieve your own illusions" rule doesn't apply, just like how you can't naturally see something you cast Invisibility on if you can't normally see invisible things; both this spell and Invisibility are [glamer] spells with no saving throw to disbelieve, so they should work similarly in this regard), if the caster has Trapfinding or something similar, then even they believe with absolute certainty that there's a trap on this item. It doesn't say "anyone other than you." It just says "anyone who can detect traps." So, you know, this probably isn't the best spell to pick up with your Beguiler's Advanced Learning feature. I mean, unless you like doing that sort of thing. Maybe you're on a diet and want to lock away the cookies from yourself without preventing your Cleric buddy from having the occasional responsible cookie after dinner (unless they cast Find Traps). I dunno, man, you do you.

The clause stating that the spell fails if another iteration of it exists within 50 feet is semi-logical but also slightly vulnerable to being gamed. First, if you just want to be a jerk, it's possible to cast the spell multiple times on movable objects that are then brought together. (Imagine several nested chests, each "trapped" with this spell. Someone opening the chests would still be 100% convinced at each level that the next chest is, for sure, trapped for real. Which one probably should be, but whatever.). Second, it would theoretically be possible to attempt to cast this spell as a test to see if anything in, say, the room you're searching already has this spell on it. It wouldn't necessarily do you much good if you can find traps, of course, since you'd still believe with unshakeable certainty that the target is trapped, but it might help a party member who can't find traps realize that they should probably turn on Detect Magic. (At which point you'd want Nystul's Magic Aura, but that at least has a non-permanent duration.)

If anything, that's the spell's weakness: it only works on characters capable of finding traps. (No, I checked: Find Traps isn't on the whitelist for Hallow.) Which might lead to some interesting interactions if folks are good at not metagaming.

I dunno where I'm going with this. I just think it's a really, really weird spell, and it's strange that I've never noticed it or paid attention to it before. Any thoughts? Any experiences with it? Any weird optimization tricks we can fuel with it?