We generally wish people on festival putting a simple-yet-convincing word happy. Surprisingly, in India, anything can be wished putting 'happy' before any word that brings a holiday in your office ;)
The question came to my mind when today I heard Happy Good Friday by a non-native speaker. I am more shocked than surprised. I'm pretty sure happy does not go with any such day/celebration(?)/event.
Though I read Wikipedia for both those days I'm not sure whether it's a celebration or showing our condolence to those respected personalities. Also, though there's good (adj) in Good Friday (noun phrase) it was the day of grief, wasn't it? I cannot say Happy [Good Friday].
Is it proper to wish Halloween or Good Friday? If yes, I'm not sure using happy there. And yes, my dear native speakers are most welcomed. :)