Translation:The witch could transform the alien into a human.
I am so struggling with some of this. I'll go for 'subjunctive' in answer to your question as it expresses the possibility of doing something rather than something having been done. Could you tell me why I can't say "The witch would be able to transform the alien into a human"? It isn't accepted, but I'm struggling to understand why it's different in mean from 'could'
I'm sick of Duo getting so picky with endings on things like Mensch, Außerirdische, and other weak-nouns. They're just nasty little traps for non-native speakers for which a kind reminder- not automatically disqualifying a question as incorrect- would be of more help for my learning IMO.