Basic Trope: A villain whose main plan is to destroy the world, and has the means to do so.
Straight: Doctor Destructo plans on using his newly created Reality Bomb to destroy reality as we know it.
Doctor Destructo plans on using a triple-level fail-safed This Will Really Destroy Reality Bomb to destroy reality, then recreating a new universe with a big bang to sterilize away whatever might have survived in some corners the bomb missed, before collapsing the new universe onto itself and decaying all matter to a state where no planets, stars or any other celestial bodies will emerge, ensuring nothing will ever exist ever again except for some stray particles.
Inverted: Doctor Destructo's sole motivation is to keep the world from being destroyed.
Subverted: Doctor Destructo's plan to destroy reality is a Red Herring meant to obfuscate his real plan, or simply a blackmail attempt: He has no plan of following through whether he gets what he wants or no.
Double Subverted: ...But once his last desire has been fulfilled, he throws the switch anyway.
The method to destroy the world turns out to be either much less dangerous than initially thought, or just completely bizarre: Destructo's device turns out to drown the Earth in lukewarm custard.
Zig Zagged: Doctor Destructo is about to destroy the world, but suddenly realizes just what an awful thing that would be to do, and stops. After attempting to come to terms with his own horridness and failing, he realizes that the only way to keep people from trying to follow his example would be to destroy himself, and the sinful world that spawned him, with his Reality Bomb.
Averted: Doctor Destructo doesn't want to destroy reality, or obviously has no way to do so.
Discussed: "In every story I've heard, the bad guys were content to rule. I think we're dealing with something bigger."
Conversed: "You'd think the villains of this show could think of something to do with the world besides blow it up."
Deconstructed: Doctor Destructo is suffering from sever depression and wants to bring an end to all the suffering around him, but finds killing the entire universe, let alone just a planet, far to difficult for any one man to achieve.