"No" antwortete er als die Tür in das Schloss fiel.

"nicht meins" at the end :)

(It's not in front of a noun, so you need the pronoun form, which has endings for nominative singular masculine and neuter.)

What do you think? Give it a try!

the vampire = der Vampir

"Is that your blood?" is one of the accepted translations.

Did you, perhaps, have a listening exercise rather than a translation exercise? If not, do you have a link to a screenshot?