A lot of ways to attack the final round. However this strategy has been with me for the last ten years. You must have a few things for this thing to work. A lot of cash, rocket engine, fireball, and this must all start on Sbadarian (stage 7). Start at the shop in the "rocks in the water" scene. Strap yourself with rocket engine and the fireball.
Go to the warp that will lead you to the scene that has the entrance to the Blackheart. Then warp to the "desert" scene. Grab the clock, then hurry back to the "Blackheart" scene. Go to the Blackheart warp then fight the Cylinder creature. You should have at least 30 seconds to your fire ball.

At the shop in round 8, go back to normal engine, or whatever speed you prefer. It will be a fast and easy road to the eighth phase of Wolfin. Pastaria will be out in one fireball. Sarcand will take 3 to 4 seconds of the weapon if you get it right. Hiyarika only takes one if you get it right. Bow Bow will take at least five seconds if you get it right. Chaprun will only take one fireball. Fuwarek will take 4 to 5 if you do it right. Sbadarian will only take one if you hit it right. That will give you around 8 to 10 seconds to spare.

Take out the spiders, then when your evil twin appears, put yourself in a position where all you have to do is kick back and drop bombs on it. When you get to that position where you can drop a arsenal on its arse, DON'T MOVE! When you blow it up, the ending will be interesting.