How do Irisalis appearance variations work?

The practical upshot is that picking a look for Irisalis is not a build decision. You are not branching into a different creature with different numbers, and you are not locking yourself out of a second form later. It is a skin. The appearance transformation mechanic is there to change how Irisalis looks on the field, and that is the whole of what it does.

This matters because a lot of games in this space tie a visual change to a real power change, so players see a second appearance and assume it is an evolution they need to chase. With Irisalis it is not. If you are building a team around element matchups, and those matchups do swing fights hard in Aniimo, the appearance you have equipped is not part of that calculation.

The system was present in the Chinese beta test, so it is a built feature rather than a concept. It sits alongside Aniimo's character creation and customization for your own Pathfinder, which gives the game two separate places to change how things look: you, and at least this one Aniimo.

Not settled: What the beta showed was the system itself rather than its contents. How many appearances Irisalis has, and what you have to do to unlock each one, is still open.