The correct phrase is: on a serious note = seriously

serious note means to be serious about a certain topic the sentence you provided does not make sense. Eliot is a dum dum. On a serious note, when does Eliot get out of prison?

Alright I checked it out. note = character Does he ever display a serious character? He asks, because the fighter is rather flippant about everything.

typo is your man ever of a serious note?*

means "On A Serious Note" often used in forum threads when someone says something off topic first and then types "OASN:" with something more related to the topic following