Drop down menu for custom page? (Not main nav menu)

I’ve tried looking everywhere for an answer to this question but can’t seem to find exactly what I’m looking for. To be honest, I’m not even sure what I’m hoping to do can be done (easily or otherwise).

I run a fansite (custom themed) and we have set up a custom page template for the individual episode pages. I want to be able to have a drop-down jump menu included in the page template (towards the top, under the page title) which links to all the other episode pages as well as each season’s listing of episodes (ie drop down of season 1 page, episode 1.01, episode 1.02, etc).

I figure I could probably do it as a form but I don’t want to have to list EVERY page in the code (particularly as there are new episodes still being created and I would have to edit the file each time).

I’ve created a custom menu where I have added all the pages I want to include in the drop-down. Is there a way to combine a custom menu with a drop-down jump menu option so that it shows within a custom page template? I don’t want it as part of the main navigation menu.

Example page link: https://www.oliverandfelicity.com/arrow/season-2/episode-2-01-city-of-heroes/

I wasn’t sure where I should be looking for help with this one so I apologise if this is in the wrong spot. Any help is greatly appreciated!

Cheers
Sez