When obtaining a Nuke Ball, press your Standard Special Move button once, and unleash your ultimate attack - it's called a Super Nuke.
Mario has quite a fancy one.
Make sure you capture that Nuke Ball!
He will start to take a pose and charge a burning ball of light. Notice that as Mario starts flashing, he transforms into Fire Mario! It's only for the length of this attack, but it might be the only way he would be able to pull this off.
Quickly, Mario shoots a giant fire blast from the palms of his hands. It travels quite fast, and more importantly: It will catch and destroy anyone who even comes near it. It can carry opponents off-screen in a heartbeat. Notice players are also getting additional damage from the burn effect.
An intense sea of flames.
One thing to keep in mind with this Super Nuke is that you can trap multiple enemies in the Fireball Finale. If you're caught in it, you're pretty much done for. If you trap all your opponents in it, you can sit back and watch the fireworks.
All three! You did well.
Fire Mario is invunerable during this move, but it takes a while before you can take control of him again. It might be easy to evade if there's just one player on the field, so try to trick them into it!