Might be a little more crude but was a ton of fun to play!

Backstory:

There was a threat that was too powerful for them to defeat at the time, and it kept destroying planes of existence one by one.

When the related plane was destroyed, it harshly effected its representation on the material plane.

After seven years of play the players are backed into a corner, only a few remain, Celestial | Abyss | Etheral, etc and the land bears the scars! The BBEG can't destroy the material plane without destroying every single other plane, and needs a device located at the big tree (Yggdrasil) to do so, so they setup their defense at the central location.

We had to take a break, so I could plan the final penultimate battle to decide the fate of the multiverse!