Random encounter

Hi. After long planning and putting my ideas on paper. And after i get my hero walking in the RPG world (well it was just a plain whitebackground) , I was wondering how to make a random encounter so that my hero can battle and train. My idea is make an invisible mc then when my guy hits the mc a countdown timer will begin and an encounter will engage… Is there any simpler ideas to go with this? Any other method you’re using? Cause you see, when i will do this method, the position of the invisible mc that willinitiate battle wuld be fixed. help please.

And also, where do i put the battle scene? My soon to be RPG is not tile based.

Thanks in advance.