Omega Five

Just beat the last stage of the game with any character in arcade mode. Shoot the heads of the trains as soon as possible. The green fire cannot be repelled and is hard to dodge. Shoot the boss when it manifests. It will explode and summon meteors which can be destroyed with gunfire.

The boss will manifest again. You should begin to use a different attack and after enough damage, the boss will summon glowing orbs that will hone in on you. You can repel these with gunfire. When the boss is low on health, meteors will constantly fall and the orbs will appear every time he explodes. The meteors will be a bigger concern then the orbs at this point.

You can also use the orbs as a shield against the meteors. When the meteors come into contact with the orbs, they will be destroyed. Since you can repel the orbs with gunfire, make sure you knock them around to destroy meteors.