In your current campaign, who's your villain?
What are its goals, methods and alignment?
What is needed in order for its goals to succeed?
My current campaign isn't D&D, but what the heck. My villain (as named by the players, since they cannot technically pronounce his name) is Space Satan.
In Ashen Stars, there is a PC race called the Vas Mal. Before the Mohilar War, they were the Vas Kra - basically the Q from Star Trek. Somehow, in the war, they were diminished.
Except, Space Satan was naughty, and locked away in his own pocked of spacetime during whatever event lessened the Vas Kra. So, when he was finally released from imprisonment ( a year or so before game start), he still had many of his powers intact. But "many" is not good enough for Space Satan. He wants it all back. Unfortunately, to do that, he's pretty sure he needs to get a hold of a chunk of spacetime from before the War. And his powers are not sufficient to do that.
Now, normally Space Satan was, on the scale of things, not actually all that bad. His focus was on usually on individuals, rather than nations, planets, or cultures. He specialized in finding some poor mortal, granting their deepest desires (without generally twisting the wish) and watching the fallout of unintended consequences. Most often, he did this to people who other mortals would probably say deserved it - their narcissistic angst over what should have happened was delightful to Space Satan. But at this point, he doesn't even know if he's immortal any more, and that's not acceptable. The depths of his sociopathy have come out, and he's going no-holds-barred to find a way back to his powers.
No culture he can reach has the tech he needs, which is most closely related to the translight-drives used on starships. He could (and is) find ways to funnel massive amounts of resources into tech research, but even taht has its limits. He's turned to the #1 jumpstarter of technology - war. He's fomenting an interstellar war to accelerate tech development to get his powers back.
Enter the players into the campaign, who frequently run afoul of his plans to start a war....
The campaign is now at the point where they have actually met Space Satan, and the campaign's final session is goign to be their response to an offer he's made to them - they get their wildest dreams, and he gets his powers back... without a war! Do they trust him? What are the repercussions of saying Yes or No?