When a comma is needed:
* If "Happy Halloween" is a complete greeting: You would use a comma after "Halloween" if it's a stand-alone greeting before a name. For example:
* "Happy Halloween, Sarah."
* "Happy Halloween, everyone."
* If "Happy Halloween" is part of a larger sentence: You would use a comma after "Halloween" if it's followed by a pause or a change in the sentence structure. For example:
* "Happy Halloween, and welcome to our spooky party!"
* "Happy Halloween, we're so glad you could join us."
When a comma is not needed:
* If "Happy Halloween" is part of a direct address: If you're directly addressing someone with "Happy Halloween," you don't need a comma. For example:
* "Happy Halloween John, what's your costume?"
Example:
* "Happy Halloween, Michael. Let's go trick-or-treating." (comma needed because it's a greeting followed by a name)
* "Happy Halloween Michael, what a great costume!" (comma not needed because it's a direct address)
Ultimately, the best way to know is to consider the context and how the sentence would sound naturally with or without the comma.