"공포영화 딱이다" literally means "It's exactly like a horror movie". 딱 is an adverb describing something looking exactly like another or two things coinciding perfectly. It is more often used with a verb, as in 이 옷은 나한테 딱 맞는다 (This dress fits me exactly), 난 이런 날이 딱 좋아 (This is a perfect day for me). 딱이다 is somewhat vague, but 이다 here is similar to "looks like", and the sentence can be taken as (이건 / 이 상황은) 꼭/딱 공표영화 같다, as in "It's right out of a horror movie".

공포영화 딱이다 It's good to watch a horror movie.