I know that "horror" is also an adjective as in I saw a horror movie yesterday. But I don't know if its comparative and superlative forms are "horrorer" and "horrorest" respectively. I searched on Google and found that these forms are used by people (mostly Indians) who are not quite good at English. I didn't find any standard source that uses these forms of the word. Please let me know if these forms are correct and accepted in standard English or not.