The phrase "boss levels" refers to the final and most difficult stages or challenges in a video game, where players face powerful and challenging enemies or bosses before completing the game. Full definition
The overall theme and mission is presented to the students, along with the quests and boss levels in order to create engagement to accomplish. (edutopia.org)
«Mighty No. 9» is a 2D platform game, with boss levels and abilities that are acquired after defeating enemies. (businessinsider.com)
This feature works in standard levels, as well as boss levels. (gamespot.com)