Megaphone Karaoke is a very good idea. The whole idea is that you have a normal Karaoke setup, but then you don’t use the microphone, you use a megaphone instead.
This does two things:
In addition to this, the megaphone can also be used as an instrument. Some of them have siren functions which are kind of annoying most times, but I’m sure if the song you’re singing to is going hard enough, and people in the spot are dancing along, you could probably use that thing like an airhorn and people would be into it (like in dance and rap music).