Master Destruction has already accomplished his goal of dominating The Multiverse.
Downplayed: Master Destruction has been to other dimensions, but conquering them isn't his top priority.
Master Destruction already rules his home universe, and conquering others is the next step.
Master Destruction believes that all our decisions didn't matter, because in another Universe our counterpart will do the exact opposite, so the only decision that matters is to destroy the Multiverse.
Master Destruction finds out that he can drain power from Universe's destruction, so more he destroys, the more powerful he becomes.
Alternatively, Master Destruction is the ruler of a Llynstan, Fork street 5, apartment 3, bedroom. Well, half of it.
Subverted: While it seems Master Destruction wants to destroy the Multiverse, he really does what's necessary to save it.
Double Subverted: ...Or that's what he wants The Hero to believe.
Parodied: Master Destruction wants to rid the multiverse of...brussel sprouts
Zig Zagged: Master Destruction alternates between trying to destroy the multiverse and protect it, due to Blue and Orange Morality.
Averted: Master Destruction wants to destroy only one Universe and dosen't know or dosen't care about Multiverse.
Enforced: “We need a epic story. How about heroes teaming up against new villain, Master Destruction, who wants to take over the Multiverse?”
Lampshaded: “I am Master Destruction! I conquered entire Universes, one after another! And soon there will be no Universe not under my rule!”
Invoked: “One of my duties as Guardian of the Multiverse is to search for all who wish to conquer it and stop them, before they become a serious threat.”
Exploited: Master Destruction is a nasty enemy to fight, but the heroes can reliably depend on him to help put down any Omnicidal Maniacs. After all, as they frequently point out, if the Multiverse is destroyed, what's he going to conquer?
Defied: Alice, who travels through alternate universes, meets Master Destruction before he tries to destroy the multiverse. She then gets him therapy.
Discussed: “With infinite amount of universes, it was only the matter of time before some nutjob gets an idea to conquer them all.”
Conversed: “Super Troper Team is my favorite comic- heroes from two worlds join forces to fight Master Destruction, who wants to destroy The Multiverse”