Click the game.
Click 'Arcade'.
Click 'Watch'
Pause the recording when there's 1:25 left.
Press
.
Click Start Playing.
As soon as you start playing, press
.
Select 'Quit Game'.
Select 'Quit (Save)'.
Click 'Arcade'.
Click 'Continue'.
Hit the boss a few times with
button to kill it.
This achievement will then pop during the credits.