The real Rizer's whereabouts during and after Project C remain unclear. He later reemerged as Mystery G. He helped his clone destroy the A.I. based on his consciousness.
Now, this is a large head. Due to its size, your movement will be restricted to a rather narrow section of the perimeter of the room. The head cannot be damaged, instead you have to destroy the four life support nodes attached to it. The nodes must be destroyed in under thirty seconds or else you get a "Game Over" regardless of how many lives you have left. C's normal attack is to release a series of explosions that cover most of the area, and if you wait around long enough, he will create replicas of Master Contra.
Get this battle done quickly, and not just because of the thirty second time limit. The replicas are very hard to avoid, especially since you have to worry about the nodes. They don't have any of the real Master Contra's special moves, they just swing the sword. However, since the room is so small it can be hard to avoid it. Roll or spin if they catch up to you or block your path. The explosions are denoted by a series of lines and a beam emitted by C, so wherever you see a the line, do not go.
You can only destroy the nodes by using lock on attacks, and it will probably take two or more full loads of beams a piece. Just run around locking on to everything and once your gauge is full, release and start locking on again.
This is the final boss of the game and quite a challenge. Actually, defeating him is not that hard, what's hard is not messing up and dying. The platform you're on is very small and at a weird angle, so it can be hard to move into the right spots to avoid C's weapons. The big head is now floating around your platform firing at you, so you will have to use your lock on weapons to hit him. He has three attacks: Launching a series of fireballs that move around the ground in wide arcs, firing energy balls at the ground which burst into rings of bullets moving outward, and firing a beam at the ground that creates a spiral of bullets that fly at you.
The two bullet attacks can be avoided just like any other bullet attack, though it is quite a bit harder now. The rings of bullets are fairly few in number (Red Falcon's Head and Brain created more), though there still is enough to make things difficult at times since your movement is so limited. If you can not move out of the way use the spin-dodge. The spiral attack is much harder because not only are there so many more bullets, but they move in a circular pattern rather than straight lines. Avoid them by staying in between the bullets or using the spin-dodge repeatedly, however be careful of ending a spin right as a bullet hits. Occasionally C will fire the beam horizontally, which does not create any bullet spirals.
Avoiding the fireballs can be quite challenging, and will probably be the most common cause of death in this fight. The fireballs generally move outward as they make their arcs, so hypothetically there is a spot in the middle of them where you will be safe. Get into the middle of the fireballs, but just get ready to move if you see one coming.
Fortunately, you can use your lock-on beams against C, so you do not have to worry about aiming. Just do what you always do with bosses like this - hold down the lock on button and release when all of your beams are locked on. You do not even have to bother sweeping back and forth to get them to find their target since running around will take care of it for you. For the most part you will be too busy avoiding things to worry about attacking after he fires, however there is quite a bit of time between attacks since C moves from one edge of the platform to another quite often.