- Think of Stage 4 as a vertical presentation of the first stage of Gradius. Rather than dealing with terrain above and below you, it will be to the left and right of you. Enemy releasing domes and walking cannons will dot the landscape on either side, including the occasional rock spewing volcano. The first power up opportunity that you are presented with is a Force Field, so make sure you collect it. You may also notice that in addition to the missiles that you fire to the left and right, you also begin to bomb into the landscape beneath you. While it doesn't have much practical application, it can bomb some of the hatches which release Ugu ships.
- Once you get beyond the dirt, you will pass through a small open section before a hail storm of gray rocks fills the screen. Stay near the bottom of the screen, and preferably toward the left side where the flow of rocks generally seems to be weaker. As these indestructible rocks fall some Ugus, both gray and gold, will fly up from the bottom. While you may reveal power-ups from the gold Ugus, particularly Options and Lasers, do not recklessly fly over to them to collect them. Make sure that the path is safe from falling rocks above before you attempt to collect them. Ironically, if you have a full complement of Options, Missiles, and Lasers, and you fire constantly, you can slow the screen down and make it a little easier to navigate.
- After the last boulder flies by, you will be presented with the choice to go down three different paths. No path is any better than another, although the left path tends to be the straightest and least interrupted. There are occasions where the paths reconnect and split back apart. If you are concerned with points, have a fully array of Options and have collected enough Speed Ups, it's possible to stretch yourself all the way across the bottom of the screen, and have weapons firing in every pathway.
Boss: Valis Fortress a.k.a. Center Core
This is easily one of the most difficult bosses in the game. Although it is entirely motionless, it uses a form of defense that it nearly impossible to avoid. The three cores at the top of the screen are all protected by three layers of shields. These shields are easily removed, and can even be destroyed before the boss attack fully begins. This occurs when the cores begin to send out blue orbs. These orbs bounces around the fortress on a trajectory determined when they are fired. It doesn't start out too badly, but eventually the room becomes full of blue orbs and dodging them all becomes nearly impossible. There are two strategies which are known to work against the fortress. The first method is very safe, but incredibly slow and boring. It is possible to wait this entire boss out and survive the whole ordeal if you park your ship in the lower right hand corner of the fortress (shown right) before any orbs are fired. You will literally have to sit there a few minutes and wait for the cores to open and shut before the fortress self-destructs. While boring, this strategy will allow you to survive the fight.
If you wish to be more aggressive and active, you will need at least two Options. Prepare yourself by removing the shields before the first blue orb is fired, then park your ship halfway between the middle and right core so that at least one option is lined up to fire at the right core. Let the first few blue orbs fly out and wait for the cores to open up. When they do, begin firing and let the option remove the right core. When it is safe to do so, zip over to the space between the left and middle cores and let your Option remove the middle core. Then fly left below the left core, and back to the space in between, and let your option remove the final core. It's not easy, but it's safer than occupying the space in the middle with all the orbs.