It's definitely something I don't need to worry about right now, but we'll be coming to a point where "The shadowy puppet master hiding in the wings" could get his reveal.

Basically my players are jumping from one universe to another, with the help of an Ancient Silver Dragon, who resides in a mountain fortress bound to the Ethereal Plane, and her sentient Well of Many Worlds that accompanies the party (think a Teru Teru Bozu). Some entity is amassing major players from each Universe to do their bidding, they're currently intangible (ephemeral?), but able to cross through different worlds and communicate with certain individuals. For an example, one of the PCs comes from Shadowfell, and his BBEG is literally Alcina Dimitrescu from Resident Evil (I got the statblock, and my family adores stuff like that in our Sessions, lol).

But the more prep work I do for the campaign, the more it feels like Vecna doesn't quite fit, and he's kind of an obvious cop out. A Lich sounds so close to perfect, but not that sweet spot. So I ask, who, or what, would be gathering a "League of BBEGs"?