Ancient Gem has a bit of a different approach from my other freeshells so far. It has an intentionally unmoving face, meaning that all of its expression must come from head and arm movements! Or, alternatively, the color of its gem eye.
For this reason, this shell doesn't follow the standard list of expressions, because they aren't really possible to convey. Instead, it has a few different head angles, with left/right or up/down tilts for all but one of them. Additionally, this shell has individually poseable arms. The same arms are available on every surface via \i[] tags, so you can make any combination of head and arms that you like!
The gem eye is set up as a dressup, but you don't have to keep it as a color for the user to pick. You can lock off the dressup menu and use it for your own purposes such as conveying a status over time, or convert it from a dressup into an animation called by \i[] tags and use it for additional expression in your dialogues. Or you can dispense with the colors altogether and just pick your favorite! The matching Ancient Gem Balloon has the same gem colors, so you can make it match the eye if desired.
Also worth noting is that that body is fully rendered under the arms, so you can also adjust this shell to be missing one or both arms and use it that way, if you like. However you'd like to use it is fine, it's very flexible! I think you could get a lot of mileage out of recoloring it to suit your setting as well (there is a PSD provided to help with this).