Ah, Seyton. One of my favorite interpretations of the play is that Mackers falls even more utterly under the devil's sway beyond the witches, and that his major domo - Seyton - is, indeed, the Prince of Darkness. It makes for a great bit of glowering stageyness for the character - and gives you a good reason to have him serve as the third murderer of Banquo, too.
And Mackers' first bit there is pretty depressing - no friends, no loyal followers, and a life faded. It's tough out there for a tyrant.
They really relied on the doctors (wizards, whatever) back then to cure their patient of all sorts of things! :D
I'll admit, I kind of blanked on the doctor for a while. Maybe someday they'll have a proper Middle Ages physician/scholar minifig for these purposes. Or, better yet, a headpiece for a plague doctor, with that full mask with the duck-like proboscis filled with herbs and whatnot to protect from "bad odors."
"I'll put it on! Send out more horses!" Seyton may be prince of darkness, but clearly there, Macbeth thinks he's an idiot. lol.
I looked in the modified heads available on BrickLink and there is 87560pb01 - that looks a little odd but with all that decoration could easily be taken for a mask to ward off bad omens and suchlike. ;)