I had an idea for a fun class, which might even serve as a possible alternative to making "mirror classes", or maybe just on its own. They would be magical painters called Maestros.
While most classes do the majority of their work in combat, the Maestro actually does most of their work as a "study" and a painting prior to combat. Their skillsets would be called painting, framing and study.
Here's how they would work in theory. You would start a sketch of another player, such as SKETCH SHAMAN ILLIDAN, which would give you a painting of Illidan as a Shaman. From there, you would use various artistic abilities to shade and paint in Illidan using different Shaman skills. In combat, you can summon and operate the painting, using any Shaman skill that matches your skill level in study (which might have some other abilities, such as memorizing someone so that you don't need them standing there to do your painting, but its main purpose would be to limit which class abilities you can use in PvP). The catch is that your magical painting of Shaman Illidan (or whoever) can only use these abilities in the same order that you drew them in. So although the Maestro essentially has access to every offensive class skill, if your expected rotation doesn't match up more or less perfectly with what your target is doing, your offense will go out of whack.
Using the framing skill, each time you use balance, your magical painting will go to the next step in its rotation. There would also be key points, such as one every 4 or so attacks, that you could refer back and forth to with a cooldown, so it wouldn't be 100% linear but it also would naturally limit you from using that classes' abilities completely freely.
In application then, each time you use the main combat skill in framing, your magical painting moves one step forward in its list, using the next attack on it. Utility skills for the class would include casting (painting) reflections as a defensive ability and probably also something like in-room glyphs, as well as "landscape" and "still life" paintings as utility skills. So if you presented a painting of an area, it might show a certain number of vnums of rooms in the area (displaying the in-game ansi map) and if you touched the vnum, you would be transported to that vnum. The areas that could be painted would be those that have been studied and therefore inserted into your list of memorized study items. Still life paintings would create food and medicinal items. The class would use up a lot of ink, so you would in essence be turning ink into pills, food or to generate your offense generally.
The idea would probably need a lot more work to function in application but one side effect might be that, in having access to all class skills in an awkward way, it would partly balance out the shadow vs. spirit thing in group combat. So if shadow wants Luminary absolve or something, they can just use a Luminary painting that has absolve attempts at a key point, or even 4 or 5 times in a row, then have it hop to the absolving point when they think it is time.