IMO this card is brilliant.
I think it will greatly increase monos for people with enough score to upgrade cards (Generally rainbows)
Why?
Mono Entropy will be able to Mutate (and lyncanthropy, but it seems like a waste for a one time effect)
Mono Time will be able to use Immortality
Mono Water will be able to use Lobotomise/Poison
Mono Air will be able to make fireflies
There are many more examples, but I dont want to list them

On the other hand it seems OP
Purple nymph with 0 cost for its skill?
Really any other nymph?
Butterfly Effect?
Flying Eternities?
Mutation skills, such as steal?
I think it would be fairer to make it cost 1 of your mark. Comments anyone?