also: ハッピーハロウィーン
expression
happy Halloween
A direct loan from English, used as a seasonal greeting around Halloween. Common in decorations, social media, and casual conversation.
ハッピーハロウィン！今日は仮装パーティーだよ。
Happy Halloween! Today is the costume party.
街中がハッピーハロウィンの飾りでいっぱいだ。
The whole town is full of Happy Halloween decorations.
Borrowed from English 'happy Halloween'.