Stage 4 has a similar layout to the first stage: two horizontal sections joined by a vertical drop. Each section will introduce one of the hardest enemies in the game. A variety of different colored masks will greet you at the entrance. It won't take long before you reach the first ammunition room. While you're in there, two yellow masked enemies will drop down from the ceiling. Remove them and jump up to the peak of the highest column. Shoot to the right, and you should actually be able to remove the first of the newest enemies, the bat-like Gelzos.
It is worth any effort to remove the Gelzos as early as possible. Once they get flying, it's extremely difficult to remove them until they decide to dive towards you. After shooting the first one, drop down to the next column. Fire off a bullet to the right and jump after it. If done correctly, you should also be able to nail the second Gelzo before it takes off. After that, however, you'll have to prepare for a battle with the rest.
Walk to the tree stump to your right, as three more Gelzos take to the air. Jump on the stump and wait for the Gelzos to fly to both the left and the right. After crossing above you two times, they will begin their attack by slowing down, and diving at you. You must be prepared to fire at them as soon as they are within the range of your gun. If you are too late, you will get hit and lose half of your health meter. Take out those three, and walk to the next ammo door. Some human enemies will approach while one more Gelzo will fly above you. Wait for the Gelzo to dive, then shoot it. That will be the last Gelzo you need to worry about for a while.
When the coast is clear, enter the door to get machine gun rounds. After only a very short walk, you'll reach another ammo door, this time for regular bullets. Shoot the enemies that comes out of the lower door first, then jump up to the door. Be careful of the enemies which come out of the next two doors, and jump up the set of gray columns. On the other side of the columns will be a green masked enemy, a grenade tosser that takes two shots to beat. Be careful because if you wait too long to attack him, he will get into a steady rhythm of lobbing grenades at you, and you'll have to back up to clear him away. Jump over the column and knock him out.
You will now be in the vertical section, but it's very short. In fact, you can fall most of the way through it without having to worry too much about getting attacked. As you fall, ninjas will appear. You can only safely fall through their appearance if you hold the joystick right as you fall. When you land, remove as many of the ninja threats as you can, then drop to the bottom and continue to the right.
As you proceed along the new horizontal section, you will be attacked by a set of regular enemies, ninjas, and Blogas. Do not attempt to travel too far with too many threats on the screen at once. Remove them and proceed slowly so that the enemies can't gang up on you. You will reach another ammo door before you need to jump up on to the tops of some columns. After another ninja appears above the columns, a few black panthers will be roaming the ground below. Continue walking right and you will approach another staircase of columns. One more panther will leap from the top, and you should safely walk below it as long as you don't stop.
Beyond the next set of columns, you will reach a bed of lava, where a new enemies lives, the Fire Men. Fire Men leap above the lava with ease. When shot, they break up into a set of three flames. The flames that land on solid ground turn into new Fire Men and rise up to the ceiling, creating a second threat that Albatross must avoid when attacking these enemies. From the highest column, you must leap over to the floating platform, while watching out for any Fire Men that approach you. Jump from platform to platform until you reach the next set of columns. Realize that not every Fire Man that appears will actually threaten you.
When you land on the next set of columns, a ninja will materialize above you. Remove it before leaping to the next set of platforms. When you land on the second platform shoot to the right in an effort to hit the next Fire Man that is about to approach you from a safe distance. Another Fire Man will leap below you. The next one has the potential to harm you, so be sure to shoot it before you leap up to the high platform. Many Fire Men after that will simply fall into the lava below.
When you reach the end, you will see a set of columns creating a downward staircase. Two Fire Men will be bouncing back and forth. Once again, it's important to shoot at them from as far away as possible so that you don't get hit by the fire that they create. Once the two Fire Men are removed, the coast will be clear and you can approach the level exit.