Apocalypse Right Now

They thought it couldn't get any worse, yet somehow, it did.

The virus that created the undead that roamed the overworld somehow started to mutate.

They got stronger, faster, and smarter than they were previously, though a few zombies never mutated or did not mutate as much. 

The mutation appeared to have carried over to skeletons, piglins, husks, and various other hostile mobs, and enhanced them in much the same way. 

The Modern Builders, the descendants of the Ancient Builders, had no choice but to flee to other dimensions. However, the virus was in the Nether and in the End as well, but fortunately, other dimensions were discovered, and they fled there; however, they may have brought the terror with them.

Not only that, but several things started emerging from the portals into the Overworld. Something eldritch... Something demonic... A plague on both houses... 

The thumbnail is from Sonic Zombies. 

Also, I originally wasn't going to release this to the world, but then I came up with a story for this thing.