The final stage takes place atop a construction site, and you will be walking along a girder that extends across the stage. When you begin, a Strangler will approach you. Depending on how quickly you move to the right, you might be approached by a Hit Man Joe from the right if you are slow.
After the screen has scrolled a short distance, the Stranglers will display a new behavior unique to this stage. They will jump up and hang on to the girder that you walk along. While they remain hanging from the girder, they will grab your ankles and drain your energy just as though they were grabbing your throat. You'll have to shake them off if they grab hold of you. As you walk forward, stop to crouch kick off anyone who arrives in front of you. Try to ignore the ones behind you until they pull themselves up and end up walking behind you.
When you see a girder hanging above the one you're walking on, and some nun-chucks on the floor, the hanging Stranglers will stop. Instead, a Crow Bar will be waiting to leap down and attack you. A second Crow Bar will approach you from the right. Take them out carefully, the nun-chucks should help. Then you will proceed forward, and a Hit Man Joe will be waiting for you from another high girder. A second Hit Man Joe may appear from behind you. If you want, you can successfully move forward and ignore both of them, stopping only to squat beneath the bullets that they fire.
You will notice a break in the girder. Jump over the gap, and you will arrive at the final boss. Any enemies that were following you will turn away.
Boss: Big Boss[edit]
Also known as the Giant Devil. The Giant Devil doesn't require a particular complicated strategy. The thing which makes the fight difficult is that the boss can arbitrarily block many of your attacks. In order for your punches and kicks to land and do damage, they have to hit at just the right time, in just the right way.
The Giant Devil will attack you with a lunging kick, or by picking you up by the head and punching you back. His attacks will send you backwards. If you happen to fall past the gap in the girder, you will grab it before falling off, and pull yourself back up. You can never actually die from falling off the girder.
In general, you should try to jump kick him from a good distance so that you are on your way down when the kick connects. In attacking this way, you will bounce back far enough away from him even if the kick doesn't connect. On occasion, you may land at just the right distance to deliver a series of standing kicks that will always connect. After around four or five hits, however, he will go back to ignoring these attacks.
Once you successfully knock the boss out, you can approach the lever on the right to lower your girlfriend and finally rescue her. Congratulations.