The thing that I love about this is that you have to play through the entire game to get to the extra scene - no easy way out using the Level Select cheat (C, A, Left, Right, B, on the menu screen and you should hear a sound). You get to the extra scene by successfully completing the Intermission Game to obtain a number which will form part of the code required to get through a locked door at the end of the game. The code contains four numbers, meaning that you must complete the Intermission Game four times.
You get to the Intermission Game by grabbing the Liberty Head on Headcases throughout the game, symbolised by a 'B' (presumably for 'Bonus'). The only problem is, once you get a Liberty Head, it disappears off whichever Headcase you got it from, so you only have six chances to win four Intermission Games - not easy. Here's where you can find each Liberty Head:-
Now for the Intermission Game itself. When you enter one, you'll appear in a small area with two machines firing basketballs, and two rows of basketball nets. You're aim is to get basketballs into nets with stars above them. There are also other types of nets. There's the net with a basketball above - this will increase the number of balls coming out of the machines. The net with the 'Back' symbol above slows down the nets, giving you a better chance to score. You should avoid the net with the Dark Demon sign above, because this will destroy one machine below (first no. 1, and then no. 2). If all machines are destroyed, then you lose, and the game ends. The game can also end if your health becomes extremely low, or if you cancel the Liberty Head (be careful - I've often done this by accident).
At the beginning of the game, you'll be given a target - a number of times you must score. The first one is 5. As you complete each Intermission Game and receive a number, the target will increase by 5 (i.e. first you must score 5, then 10, 15, and 20). Also, the bombs, that sometimes appear in the place of basketballs, become a lot more frequent, so watch out.
When playing the Intermission Game, don't just recklessly try hitting every basket ball that flies out of the machines. Instead, keep an eye out for the Dark Demon net, hitting balls only when there's no chance of them landing in it - you have infinite time, so there'd no need to rush. I've found that if you hit a ball to the left, when it's in line with one of the lower nets, it will remain in line and score when it comes down.
Once you obtain all code numbers, complete the ordinary game and wait right through to the end of the credits. A password screen will appear asking you to enter your four number code. This will open the way to the extra scene, where it's time to get your own back on the greedy boss responsible for putting on the play that caused you so much trouble.
You'll begin by entering the boss's office. In a moment, he'll bring in some of his thugs to take you out, but they're actually standing just outside the screen, meaning you can hit the one on the left quite a few times before he actually enters. When they do enter, they'll start throwing money at you which can take off about a quarter of your health. You can dodge this by jumping through a gap between the money once it's low enough.
The thug on the left should be taken out soon enough - he'll run round the screen a bit, then disappear. This reduces the amount of money being thrown at you, making it easier to dodge while you take out the other thug.
Once they're gone, you can start hitting the boss. When you do hit him, he'll throw money in the air, except that this money will home in on you. To dodge this, hit him from one side of the screen, then go as far to that side as possible, and when the money starts falling, run all the way to the other end of the screen. You should be able to just about dodge all the money being thrown at you.
After several blows, the boss will get really angry. Just hit him one more time, and he'll be taken care of. Well, now you really have completed the game, and there's even a 'THE END' sign to confirm it.