"Two cups of coffee, black, please."
Translation:Kaksi kuppia kahvia, mustana, kiitos.
But isn't black coffee just musta kahvi, not "coffee blackened" which makes no real sense in English
"Coffee blackened" would be something like "mustattu kahvi", which to my knowledge doesn't exist. (Onneksi.) :)
"Mustana" is the word "musta" in the essive case which e.g. marks being (as) something. "Mustana" - in the state of being black.
"Sinuna en söisi tuota." - I wouldn't eat that if I were you.
"Huolestuneena kansalaisena..." - as a concerned citizen...
You might also see this case in expressions such as "Tänä aamuna posti toi minulle kirjeen" (This morning I received a letter in the mail), etc.