TTRPG DMs, what ideas do you have in your back pocket for campaigns?

Idk if this goes here since this category is mainly for *video* games, but I'll try here anyway, cuz idk where else this would go.

So I don't get much opportunity to play ttrpgs outside of a DnD 5e group local to an area adjacent to mine (in which we meet twice a month for one-shots and two-part campaigns), but I've been meaning to get into playing PathFinder 2e as both a DM and a player, as well as a few other systems. I've got a few ideas rn, but they're not really significantly fleshed out, just kinda floating in my brain. I've got the following:

• A wild magic dragon that was created artificially by a magic cult as a sort of super-weapon. Depending on which elemental magic it casts, it's opposite becomes its weakness. (Ex. It casts fireball, it's weakness becomes ice, etc.) I think it would be a fun secret boss.
  
• A sort of living wall boss fight like the one in FF12. A long, narrow hallway with only one exit, and a big, slowly moving wall that's really mad at you. Not very original, I know, but I still really like this concept.
  
• An enemy NPC that travels between dimensions (tt systems) that always seeks to battle the party like Gilgamesh. So they could appear in DnD, Pathfinder, Lancer,  etc., but they're always the same person. Their form changes to fit the system they're currently in, but they always find a way to have more than one set of arms.
• Saint Archibald's Mace of Focus: A mace with a crystal for a bludgeon. The crystal eminates a soothing aura that calms only the wielder. It grants the wielder resistance to rage and other effects that would cause a loss of focus (haven't worked out what those would be yet). Possibly an early-mid level item (like, 5 or 6).

 Anyway, those are my ideas on my back pocket. I'm curious about what you think and what you've got in store for your players. Ciao for now.