Whether or not we call the ability passive or active is a matter of semantics, more or less. The key feature here is that it can continuously change its available skill each turn. E.g. its like an auto-mutate effect except only the active skill changes while the base card and stats remain the same.
Its a fun effect and fits the theme of
pretty well.
My only critique would be that picking skills that don't currently get used by mutate would help keep it distinct from mutate and fallen elfe / druid. That would help it to bring something new to the game.
I'm not sure if this has been done before or not... The mechanic seems familiar, but I don't know if its been done in quite this way.