The secret area N-1 houses one secret boss from Zero 3- Omega Zero. People who played that game know that this guy is using Zero's "origional" body. Anyway, once you take down this guy, go to the area where you can fight bosses from Zero 3 and 4. Take the third door and follow it through. Eventually you'll reach a strange stone that looks alot like a live metal.
Go to the lab in X-1 and talk to fluub (in the Lab area). After the game, he'll analyse it and find out it's a live metal, letting you use Model OX.
NOTE: You do NOT have to beat the 8 bosses from Zero 3 and 4 to fight Omega Zero or get OX.
Beat Omega zero in area N-1 and find the live metal. Take it to fluub to get OX
Start by heading to the teleporter that is placed before level C-1 . Then, enter that level and proceed until you find a green door, which you should enter. Use the human form of your character to go under the gap and then get the 3 items on the right, which include 1 life.
Now, go back to the teleporter (which resets the position of all items in the levels) and repeat the step above, something you can do until you have up to 9 lifes, the maximum value for them in this game.
Beat the high score on Crusher-F (100 points)
Defeat any two bosses