Vile has his own stage! Reach it by finding one of the teleporters in Blizzard Buffalo, Volt Catfish, or Crush Crayfish's stages.
Start by going right and taking out the Notor Bangers, then head down and fight the Wall Cancers. Go right and into the elevator. If you defeated Volt Catfish before coming here, the elevator will move. Otherwise, you'll have to wall jump up, avoiding the debris. This will bring you up past several life pickups. You shouldn't need these at this point. Getting out of the elevator is inadvisable because it leaves you vulnerable to debris. Once you reach the top, go right. Take out the Hamma Hamma with a Triad Thunder, then head up the ladder and into the door.
Vile in Ride Armor
You'll have to fight Vile twice. Once in his Ride Armor and once without it. Both are weak to Ray Splasher and Spinning Blade, but you might run out of ammo if you only use one of them. Like the Nightmare Police, you'll have to deal the final blow with a weapon he's weak to in order to completely destroy him. Doing this will give you an alternate version of a later stage, along with different boss fights and the opportunity to get a very powerful weapon that will make the terrible final boss much more bearable.
Vile's Ride Armor is a variation on the Kangaroo Ride Armor. It's actually a very simple first round. He just dashes left and right, hitting the walls. Wall jump over him, land, turn and unleash a charged shot or one of his weaknesses, then jump on the next wall and repeat. The Spinning Blade is pretty handy here.
This battle is similar to the one in the first Mega Man X
game. He can jump pretty high, shoot a flurry of small shots, and a wave of fire that travels across the floor. Avoid these attacks as best you can. It's best to use the Ray Splasher against him. Remember to finish him with that or the Spinning Blade.
Don't rest yet! You have 50 seconds to get out of here before the factory explodes. Don't bother to fight the enemies. Just run through or past them. If your health is low, grab this one large health pickup before the drop, or use a sub tank. Avoid the items, they're just there to distract you. Use any leftover Spinning Blades on the Drill Wayings. They'll be destroyed in one hit. I hope you defeated Volt Catfish, because this elevator might mean the difference between life and death. Dash jump and air dash past the collapsing floors. The third one leads to a hole, so make sure you can get enough air to make it across. Get to the right as fast as you can and hop into that teleporter! You'll end up back in whatever stage you used to get to Vile. Phew!