Novel and ff ideas for authors

A last boss from some game reincarnated in a fantasy medieval world that has machinery.

And when that world faces this boss they will know the horror of facing the last boss with its boss music, and when some people succesfully killed the last boss they will know how difficult it is because it will revive, and will enter its second phase to fourth phase.

And even if they killed it in its fourth phase it will ressurect with a cooldown of days, months, or even years or decades but that boss will become stronger each time it died and its boss music will be updated to a new one and gain a new ability.