"It is possibly a green elephant."
Translation:Det er muligvis en grøn elefant.
That is a good question, and I don't know if I can answer it properly. But I am going to give it a try.
In the sentence, THE correct phrase is "DET er muligvis en grøn elefant". This is at first contra intuitive since elefant is common gender (EN elefant), and you would for instance say "DEN elefant er tyk" (that elephant is fat)
But in the above sentence the elphant is not the subject of the sentence but instead what we in Danish call the subject's predicate, and here the gender of the predicate does not necessarily influence the gender of the subject (den/det), at least when it comes to "kopulative" verbs (for instance to be="at være", to be called="at kaldes", to become="at blive" etc)
Instead the subject in this case is a pronoun reffering to another sentence. For instance "What is it? - It is possibly a green elephant". And as it happens, you always say "hvad er det?" in Danish, never "Hvad er den?"
I think this is confusing mainly because of the pronoun. For instance "DyrET er EN elefant" should be pretty straight forward.. Hope it helps