Board Thread:Ask the Staff/@comment-27065637-20151107203749/@comment-508329-20151112073854

The rules for fusion design seem to be pretty loose and flexible, but the design choices seem to follow some trends.

If a fusion is supposed to be unstable, the character design will probably include some visual cues to suggest the idea of instability, which is probably why Malachite looks so monstrous and Alexandrite looks so disjointed.

But if they're designing a stable fusion and decide that extra limbs are a really good fit for the character, or they're designing an unstable fusion and decide that the character design works better without extra limbs, they can do that too.