Player must defeat the worst of the worst in the arena of Boss Mode.
You have to defeat all 5 bosses in the game, in a row with one life. You also have to go solo otherwise it won't unlock. Each defeated boss will leave an item to fully recover your health. Try to leave them on the ground and use it only when you have just the last drop of your blood.
The first four bosses follow a simple fight pattern, they don't always do the same thing but you will work out what happens when you fight them. If you can leave several of the health items on the ground just in case you need them with the final boss.
Once you get to the final boss keep at a distance and let him approach you. When he is within hitting distance use the YYYYY combo to attack. Once hit move out the way and repeat the same moves until you kill him. At points the last boss will fire on you none stop, just keep avoiding his bullets and repeating the combo when possible.