One of the 1st steps I do when I think about a new campaign is the Big Bad Guy. The too-often Shadowy hand that pulls the strings of the evil/insane/chaotic side of the game. Creating a good bad guy that will act as a motivator is not easy. If he’s too powerful early on in the campaign, the players risk being humiliated more than challenged. And humiliation, while a very powerful motivator to get even, is never a synonym of fun for the players.
I tried it in our 1st D&D 3.0 campaign, where an evil, unkillable (at the PC’s level) Gargoyle terrorized a village and forced the characters to perform quests for it. While the players wanted to kill the gargoyle really bad, the motivation was based on coercion, something that should not be done often or for long periods of time.
My 2 best villains were created more or less by accident and had this common theme: They were slightly stronger than the PCs and were able, time and time again to flee right before abject defeat at the hands of the PCs. They grew in power during the campaign and were the front man to the hidden overlord/power.
So for this campaign, I plan on doing something slightly different. The Big bad guy will have a name and a clear agenda. It will actually be a minor villain that the player’s defeated in the conclusion of our former High Level campaign. Since the new campaign shares the same Homebrewed world, the defeated villain will plan it’s revenge on the whole world once the High Level PCs move on to other planes for further adventures.
The new PCs will know early on who and what this new villain is. But being so much less powerful than it, the PCs will not register on the villain’s radar for quite some time, allowing them to build up their power and reputation, leading to a climatic confrontation much later in the campaign.