You know what else has no physicality?
An image.
Like a tattoo or a picture drawn on a page. Both of which work.
Are you even reading what I'm typing here? What if..................you need to PHYSICALLY press the tattoo to the vault to open it? No illusion that the party can cast will be able to do that.
Also, you're wrong about the tattoo. The inks have physicality. The skin has physicality and for all the party knows it takes both.
You know what else would work? A temporary tattoo.
That is not necessarily true. It might require permanent inks. Or special arcane inks that the party doesn't have. Or...
RAW, RAI, Illusions work because it's an image. Not a physical key.
Is there some part of "Only the DM knows that" that you are not understanding from what I am saying here? I've said that three times now and you keep bringing it back up as if it changes something. There is no way for the party to know that by
looking at the tattoo.
an Illusionist could open the door with the Creation Spell.
He doesn't have that spell, because he's too low level. There's a reason why I said "that the party can cast." You seem to have missed this at the top of the first page. "
An Adventure for 4th-Level Characters" But hell, even if the group was 9th level and could cast creation, you cannot create a tattoo with it.
Or if you wanna look at 3rd level, there's always Phantom Steed which makes a freaking HORSE you can RIDE.
That's not a tattoo. Not that 4th level PCs can cast that spell, either.
Wait?! You're actually arguing that because there are two illusions that specify that they have physicality, that the rest of the illusions which specify that they do not have physicality have physicality?
Here is what a 4th level PC can cast.
Minor Illusion(cantrip): "Physical interaction with the image reveals it to be an illusion, because things can pass through it."
Disguise Self(1st lvl): "The changes wrought by this spell fail to hold up to physical inspection." - so that isn't physical at all.
Illusory Script(1st lvl): - Doesn't specify physical or not, so according to Crawford it is not. Also doesn't make tattoos. It's writing.
Invisibility(2nd lvl): - Not capable of making tattoos. Has no physicality in any case.
Mirror Image(2nd lvl): - Same as above.
Phantasmal Force(2nd lvl): - Same as above.
No illusion spell castable by a 4th level group(even if you have a caster that can cast them in the first place, can take the place of a tattoo that needs to be there physically.