What case is "goscia"?
Yes. Mamy kogo? co? (We have whom? what?) = Accusative.
yes it is accusative
Why isn't it "goscię"? Or does this only apply for real female and not words with an a at the end which are masculine?
But this word doesn't end with -a. Well, this form (Accusative) does, but not the basic, Nominative one, which is "gość".
The masculine words ending with -a also get -ę ending in Accusative.
Ah! Ta again.