Ah, finally got decent access to respond...
Why would a homunculus be related to 
Darkness (outside of FMA)?
Why would a homunculus be related to alchemy (outside of FMA)?
Aside from all that, this card idea seems to make the nymphs lose their... unique qualities...
Maybe you should analyze what a homunculus really is and how it can be integrated into the game without too much influence from another franchise.
I am familiar with FMA, but that's not exactly where I got the concept from for its typing. As I describe in the notes, alchemy, at least in other works I've read, has often been described as a darker study. Also, as depicted in the aforementioned, but not limited to, FMA, the use of humans or the creation of living things artificially is often regarded as taboo, hence
.
As for ability, as described in the Wiki links provided by ET, homunculi are usually borne from alchemical attempts at recreating life. Also, as I described in the Note, a creature born from alchemy should have a tiny bit of skill in it.
Entropy mark is too powerful compared to the other options.
Yeah, I realized that earlier. As soon as I have access to my computer, I'll edit the costs.
An idea I had rather late was simply to make the spell replace the ability. It would take the initial
/
to gain the skill as described in the Note, but the price would change to costs shown on the cards, if not equal to the Nymph's ability cost.
