Villain motivations: Pure destructive drive
Creating and running an RPG villain can be a complex endeavor, but the villains themselves don’t have to be complicated. Coming up with involved antagonists takes a lot of time and thought, and playing them can be difficult. All it takes is a core motive, though, and as you portray the villain, they develop naturally.
So what makes a villain do villainous things? Pure destruction is a simple desire, but selling it to the players can be hard. I mean, who wants to destroy the world for no reason? That would be pretty silly, but you can make it work.
You don’t have to, though. What are some good reasons a person (or thing) would want to destroy everything?
Let’s start small, with something not so epic; a BBEG who doesn’t want to crack open planets or wipe out realities. Alucard of the Hellsing series springs to mind. While technically the protagonist of the series (and note that protagonist and hero are not necessarily the same thing), Alucard’s desire is, to quote the vampire himself, to “revel in the destruction.” He’s old and bored, and he’s so powerful that nothing has been a challenge for him in a long time. He serves the Hellsing Organization and picks fights with villains just because he’s looking for a good fight.
A villain like an immortal might be searching for relief of ages of ennui. They might even be looking for someone who can kill them and end the torment of immortality. Enter the player characters. Surely raising an army and conquering the land will call forth worthy heroes? Maybe a plot to unchain a demonic force is a bid to summon the only being that can finally kill them?
Now let’s crank it up a notch. What if the villain needs destruction to live themselves? They might need to consume souls, the lifeforce of the land, or the sunlight from the sky. They’re driven to commit what others might view as destructive acts, conquest, and slaughter, just in the name of their own survival.
It might just be their nature — or even be a force of nature — but what if we make it more personal? What if our villain has been cursed? It’s not their idea and it’s not their fault, but they have to feed. Maybe they’re even trying to restrain themselves? One time they tried to starve and let themself die, but they went into a mindless feeding frenzy. That wasteland on the map there? That was created by a poor, hangry villain. Rounding up people en masse to farm people as food might be seen as an attempt to save the world.
You can do weirder stuff, too. (And by weird, I mean it’s been done in comic books and movies and novels and everything, so you can do it, too.) Let’s say that there are multiple realities, and that the existence of the one the game takes place in threatens the stability of the others. What if the villain is trying to save entire realities of people by destroying their own? A few bajillion lives to save bazillions more. Do the player characters stop them? Join them? Can they find a way to save everyone?
If your antagonist is driven off the rails and wants to wipe out people / worlds / realities, that doesn’t take a ten page backstory to convince the player that they have a good reason.