Adventure workshopping

[Skrum]

I'm planning my next adventure, and I'm looking for some extra ideas.

The gist of this is the players are hunting a powerful caster who has (accidently, but the players aren't fully aware of this yet) made himself into a doorway to the Negative Energy Plane. He has been terrorizing the city by attacking spellcasters to drain their spell energy.

My plan so far is to give the players two rumors - one to a professor that specializes in the Shadowfell. He'll tell them what's actually happening, that the BBEG is actually hastening his own demise by draining all this energy as that's what's creating the doorway, and if he's not killed or prevented from draining more energy, an awful creature will appear. The professor will also give them a way to find the BBEG.

The second rumor I'm not sure what to do with. This guy first appeared at a party the players went to, where the players witnessed him draining spells from the guests. I'm thinking that maybe they encounter one of the other party goers, but now they've been affected by the shadowmagic and are also transforming? But I'm not sure how this becomes a lead to find the BBEG.

Any ideas?

[Kvess]

Have you heard of the Doomguard? There’s a cabal across the planes that believes that entropy is not only inevitable — decay is a good thing, and sometimes the multiverse needs a little push to keep something from existing forever and creating stagnation. The ultimate source of entropy is the plane of negative energy, which the Doomguard baptizes new initiates in.

You could have a small group of entropy cultists seeking the portal for their own purposes.