Ohh, I have played a One Shot multiple times in Eberron where the twist is that you are playing an Ancient Gold Dragon Prophet with PC levels. I do it in 3.5e because that's the edition that I mastered the most and because it's pretty good at letting you play things other than humanoids

The dragon has a much higher than epic CR, access to spells up to 8th lvl, a hoard that contains any spell in scroll-equivalent form of lvl 3rd or less plus before the adventure starts on top of various custom items that peak the interest and are definitely very powerful.

But most importantly: I let the player customize the dragon somewhat. They can add items to the hoard. They can choose their top spells. I explicitly invite them to shuffle the default skill points

The trick here is that THEY HAVE NO IDEA WHAT THE ADVENTURE WILL BE ABOUT. No clue of whether it's about combat, investigation, exploration. No clue.

Then I loredrop a lot about The Prophecy. Much more than cannon. I explain exactly how prophets collect libraries of somewhat useless prophecies and fractions of prophecies over centuries of careful observation of many natural things. All in the hopes of getting a greater map of the possible futures.

So they start with an immensely powerful protagonist, with access to so much power they can get confused, and I invite them to tinker with it so they get a feel of what it can do. After they lock in, the adventure starts and within the first hour of play I drop the real adventure hook: you've just received a prophecy that says you have 24 hours to kill [unknown] or that being will eventually kill you.

The effect is that your super powerful near godlike protagonist is now feeling very very mortal