Let me start by mentioning that the video for the last post is up! So please check it out and I apologize again for the delay.
While working on grass growth I discovered an interesting effect if I greatly speed up the rate of said growth:
Sure, this is completely useless as is, but I find the visual effect of the grass growing and reaching out to the dwarf, nearly drowning him to be quite interesting.
This gave me an idea for an end game creature for your dwarves to fight: a shadow fiend. A bodiless entity that stretches across the floors and can harm any living creature it touches. It would move with the same pattern and visual affect as the grass growth in the video, but with shadow replacing the grass. The only way to kill it would be to lure it into the light and it would be smart enough to make it near impossible to lure it out into the open during day time. So you would need to trap it using more creative methods. I do not have combat and traps yet, but once I do, I'll see to it that the shadow fiend becomes reality.