Help with building villain goals

I'm working on building up a campaign for my players and just came up with the overall goal: To unleash the fallen gods onto the plane

I'm just trying to come up with several ways to make this interesting with sub goals that need to be accomplished for instance:

Villain can obtain the 5 keys of the betrayers to unlock the gate

Villain can perform a mass sacrifice of an entire city after carving the appropriate runs into certain points

Does anyone have any suggestions? or tips for building this out...I'm really worried about falling into a too much of a trope.

I like the idea of using keys (or seals, or whatever you want to call them). 

You make it more interesting by making the ritual to release the fallen gods only able to be completed by a selfless act. 

The 13 ghosts movie and Dragonlance are examples of this. If that selfless act is performed by a NPC the PCs like, that would be better.  

Just a thought.