No. If we assume that you have to target the wall it would at the very least stop after destroying the wall. But by RAW, you can’t even cast it on something behind the wall, because you cannot target something (or someone) with a spell if they are behind total cover. Total cover is created by being behind completely behind an obstacle (like a wall). This counts even if the obstacle is invisible. Furthermore, because if you chose an invalid target for a spell, you'd still expend the spellslot but there would be no effect. So you actually spend a sixth level spell a lot to achieve nothing. I would not recommend doing it this way, but that’s what the rules say.

It’s technically still invisible. But as there is not clear rule for that I'd say it’s up to interpretation.

Yes. See invisibility should work as well. Both are quite annoying to activate when in a fight though.

Definitely. If one is trying to be prepared, See Invisibility lasts an hour but takes a lvl 2 slot while Detect Magic lasts 10 minutes and only takes a lvl 1 slot, so there's tradeoffs for sure. One of the things I like about my firbolg twilight cleric is having the detect magic racial ability, too.

Most of the time I think it's because the spell calls for a saving throw and there isn't a mechanic for what a wall's Con save ought to be. That's not a unsolvable problem by any means, but I assume that's why the restrictions exist

I'd argue you can 'see' the wall if you place something on it, like: - your hand - your frontline's hand (or some other body part) - a ghost's hand - flour, dust, tar, enemies' blood, coughing syrup, and other things that could stick to the surface - gecko, spider, and other creatures that wouldn't fall off; probably also your familiar

I think spells that target the spirit of a target shouldn't be able to be fired blind - that's what i would let it depend on. A cold ray doesn't need a visible target, but everything mind affecting that is not AoE will need it.

And this is why my group is ok saying "that rule is profoundly dumb" and ignoring it while suspecting Crawford of being involved.

* Detect magic.

I've specifically focused on means that don't require a spell slot to use. Left familiar as an exception because people like to have them anyway and it can be ritual cast.

RAW/RAI?

Rules as written, rules as intended.

The humble cone of cold:


Nope 

Nope 

Crawford also rules that See Invisibility doesn't remove the advantage/disadvantage on attack rolls because it doesn't say so in the spell's effect, so... Yeah, I always ignore what he says.

Ope great catch

By that logic you can see air because there's clouds in the sky.

Son of a bitch, that's a good argument.