final boss

noun3

1. •
   An extremely powerful enemy that a player fights at the end of a campaign or story.
2. •
   (informal, figurative) An extremely difficult thing that one needs to finish or beat in order to complete some task.

   • The kitchen is the final boss of any packing adventure. Because there are so many breakable items, make sure you dedicate enough time to packing your dishes properly. — 2023
3. •
   (informal, figurative) The best or ultimate example of something; an epitome.

   • Take one look at the tools here and it quickly becomes clear that this is the final boss of makerspaces. — 2022