Reforge

Utilize Morse code

Guard: Can you blame me with that- THING- out there? I think a huge glowing tower showing up in the valley is a pretty good reason to be freaking out!
Guard: It-
Guard: And shouldn't the scouts have come back by now? Is everyone we sent just DEAD?
Guard: Bro-
Guard: And what DID this? Why? What did it even do!? It's obviously some spirit but nobody's telling us which one or anything about it- do they not know or-

Show Content

Spoiler
You try tapping out a message on the wall, but there's no reaction. You guess they can't hear any noises you make or something like that? Which would explain your inability to get anyone's attention from the ground. Or maybe they just haven't noticed over this guy's panicked ranting.

Write on the wall, with scratches or something, like a ghost.

Guard: Bro. Deep breath. Okay. Can we, right now, do anything about this that we aren't already doing?
Guard: ...
Guard: No.
Guard: No, we can't.
Guard: I just-
Guard: Wait. What's-

Show Content

Spoiler
They can't see or hear you, but perhaps they could see something you write? You don't exactly have a precision instrument, but you should still be able to scratch out a small message.

Guard: OH MY GODS IT'S A GHOST
Guard: ...that's not how ghosts work.

Show Content

Spoiler
So you found a way to communicate, but you'd prefer to actually get some useful help rather than just spook this guard more.

You've got to get into the city and see the vizier- to deliver Donella to safety and to share what you know about the situation. Getting this guy to stop yelling would be a plus.

What should you write? It'll have to be pretty short.