I'm writing this fantasy story with the MC slowly transforming into a non-human being. Which makes him invulnerable... Or at least quite resistant. The problem is that I'm still not fully sure which the limitations should be.
- Hard to kill, with some weak point, like your typical monster (vampires with a stake in their hearts, werewolves with silver bullets, etc.)
- Or immortal with exceptions. Think Highlander, for example. So he can only be killed by someone like him (the antagonist).
Also, I planned it so the MC doesn't discover all of this until around halfway through the story, or maybe even later. And I wondered, would it demerit his previous victories if it was suddenly implied he was beyond a regular human at that point without fully knowing it? Would it be enough if I made it obvious from the start that there was something off with him?
In any case, my worry is: How should I tread the story to not make it boring for the readers because of the MC being maybe impossible to kill?