I think that too, it was amusing to make a 'gray goo' happen. The goo tends make bands around desert areas so I wonder if number break happens between forest/plains and desserts. Either way if anyone complaining about ooze eating their world some number gen in the final part world gen gets scuffed.(if you like I could take picture of it I don't know where your screen shots get sent to when I press c so it's going to be a bad phone pic, also the goo thing happened on triangle world gen version the hex one it appears but I don't think tick change over is in unless I'm blind and can't find the game control)
That actually sounds like a really cool idea. But I should probably remove the goo bug, and replace it with an actual species that is so efficient that it destroys all other life.
Maybe some kind of fungus infestation/lotus swarm. The animal version would be xenomorphs :)
An interesting thing in the challenge could be how to contain it. Maybe barriers can be built to prevent it's spread for example.