D&D General Campaign Idea, Weakening an elder evil

[Tyler Dunn]

I have an idea for a campaign, but I need some help with it

The basic premise is that a long time ago, a Lich used some magic from the far realm to make himself into an elder evil and nearly conquered the world with his undead army. He was foiled when a group of heroes managed to seal him away using powerful magic. In the present day however, the seal is weakening and the elder evil will soon be free. The players could learn of this and be tasked with finding a way to weaken this elder evil so they can defeat it when it emerges.

What I want to know is how could the PCs weaken an elder evil in a way that a campaign could be centered around it.

 

[Gilladian]

Well, does the lich still have a phylactery? He may not need it to stay alive, but it might still contain enough of his essence that destroying it would substantially weaken him. Finding said phylactery could be a lifelong challenge. Where was it made? Who made it? What does it look like? Where could it have been hidden? Who would have known where or how it was put? Lots of possibilities there.

Also, how did he become an elder evil? Did he make some sort of bargain with another being or even a god? If so, could that bargain be voided somehow? Or his tie to some form of power/energy be broken? Even if he could not be severed completely from his source of energy, just weakening it could be a blow to him.