Similar to Time Attack, you must play the "Boss Rush" mode for the original 1989 DuckTales game. In this mode, you will play the 6 bosses of the game in a given order, and must defeat them all within 60 minutes. Generally, you should not require an hour to complete this mode. 5 minutes is decent, and 10 is generous. Additionally, you do not have the luxury of lowering the difficulty of the game nor gathering heart containers to boost your max HP. However, death does not appear to subtract from your lives counter; it just will eat up your time as you wait for your replacement duck to appear and be controllable.
Just like with the other modes, you can use the "Watch" option to see how each boss plays out, and some tricks for handling each one. Note that some players may abuse some features of how the game is coded to quickly beat several bosses, so you may want to view a few slower records to have more leeway into normal completion of the game.