occidental mercury.
Whole frame of body inclining to dryness.

What does that even look like?

Wouldn't this depend on the sign Mercury is in as well? Dry can be either hot and dry (choleric) or cold and dry (melancholic), which makes a big difference in appearance and mannerisms. Dryness decreases on its own while moisture increases. Generally, this could maybe make someone shorter and thinner and have smaller features.