So I was thinking of having the MC have to bounce between parallel worlds for a bit. Wanted to have some odd team-ups for him to get caught up in. I was going to go with Annie Oakley, Abraham Lincoln and Van Helsing fighting demons on top of a speeding train in Pennsylvania. Got any weird mash-ups ideas of famous historical or fictional people? Not sure who to make the badguy. Was thinking of Keith Kellogg, the guy who invented frosted flakes.
This gives me monument mythos vibes.
I think you should use cryptids or demons that exist in mythos, basically making a story out of human stories.
You could use for the fight scene in Pennsylvania a tribe of dogmen with maybe even a thunderbird joining in?
You could use the the fantasy wiki with fictional characters or Rhaps story as inspiration for further ideas.
Another idea for a antagonist could be Zalgo (as in the fantasy wiki) and an (evil) entertainment company.
Zalgo is an entity trapped behind the dimensional wall of fiction and only has control over fiction and can create weak servants.
The entertainment company or the ceo would make a deal with him to take, idk, the world over?
Zalgo's inclusion could give an explanation for why it has to be interdimensional.
They want to do the good old 02 and destroy everything.