Very evocative! If you were to expand this, I would love to learn more about the life cycle of how this monster operates.
The mechanics with seeds and roots has a nice flow to it, but I would have liked to see more abilities that play on the forced laughter and mirth mentioned in the flavor text. I also find the Shifty Trigger a bit confusing - why is a mostly immobile tree teleporting around?
Overall a really fun read and could easily be added in any timescape adventures or grimdark settings!