Should I add character description in this scenario?

For my script, the villain is introduced in a mask, with his body covered when we first see him so the reader does not know his age or what he looks like, other than height and weight.

So I should write his name in all capitals here, cause it's his first appearance. But should I save his physical description till later, when the reader first sees his first face appearance, or should I give description when you first see him, even if he is wearing a mask?
I would tell it in the way your audience is going to see the piece. If you don't want to reveal who the villain is, then quickly describe what they're using to hide their identity and use a character name that's non-descriptive like, "Shadowy figure" or "Masked Man". Then later on when you reveal his or her identity, you can describe what they look like, but of course, keep it short and only highlight the most important parts that are relevant to the character and story. Doing this will make it surprising to the readers whom you'll want to hook just as much as the audience later on. After all, your readers will be the ones who'll want to make it into a film.
Okay thanks. But I was told before that it is unprofessional in script writing, to write it that way, and that it's proper format to write who every character is, name wise, when they first appear. Unless I can do that, and was told wrong?
The thing about scripts are that, yes, certain standards need to be adhered to, so that pre-production runs smoothly, but little nuancesthat don't affect pre-production like this are really up to the writer. As long as it's formatted properly and you're making it clear as day that your villain is hiding his identity until the end, then you're okay.

The reason why standards exist is so that your director, DP, producers, and every other above the line person can read it and univerSally agree that this is what is being shown and said, and that this is how long each scene will be.
You're splitting hairs.

You've seen "Scream" right? Have you read the screenplay? It was very hot when it was first written but it also breaks every one of the Truby rules that you're stuck to. Go and read the very first scene: Camera angles, establishing shots, direction on the page, unfilmables.... it's all there.

In that first scene, the killer is first introduced as MAN through dialog. Then, he's a SHADOW. Then he's a FIGURE. Then finally, several pages in, "THE GHOST FACE KILLER APPEARS."

TL/ DR Write it however the f you're going to write it. Just make it readable and hook your reader.