The phrase "last boss" typically refers to the final and most challenging enemy or obstacle that one must overcome in a video game or a difficult task. Full definition
They even added the SMS last boss into the arcade version. (segadoes.com)
But just translating that pose to the screen wouldn't really fill up the horizontal space of the battlefield, and it wouldn't look like a proper last boss. (shmuplations.com)
Couple that with a poor art design and presentation for the game's cinematics, laughable voice acting, boring and repetitive environments and what has to be the most anti-climatic last boss fight in the history of gaming, you have a clear recipe for failure and disaster. (levelupvideogames.net)