Interesting but i'm a bit skeptical on comparison with mutation.
seems too similar to (improved) mutation, except without stat changing, only ability change.
Otherwise to the stat changing thing, how is this is a much different mechanic to mutation?
This creature is supposed to be situational compared to Fallen druid. as opposed to it, Flux bird just take care of annoying abilities like destroy and steal and such. Lets say in a situation of a RoL (1|1) has been imbued with buttefly effect, flux bird denies the ability and gives it something else. other situation. a nice jade dragon with no abilities... until Flux bird says: nuh uh, you better get acceleration or dive, now go kill.
its a 2 cost because you can have the chance of giving your creatures an ability that would make it OP at any time! Also, i think 2 is equivalent to 1 since 2 =supernova.
It nevers says it can target vanilla creatures and give them abilities, it says "Target" ability, not target creature ability.
Your argument is solely based on mechanics that already basically exist or are similar and costs.
Does this mean it can also do the same for permanents? I suggest changing the wording to something like:
Change target creature's ability.
if you put this in aether, its just a soft lobotomizer, which can target vanilla creatures. Why repeat a similar mechanic?
Mutation still can give a random ability to a vanilla creature, so no difference there either.
Changing the actual element cost from
to
does not justify your implications of it being different.