There seems to be a lot floating round about saying 'Yes' as a GM at the moment. I have some opinions on that, but I don't think my opinions are important: you should see what works with your group(s) for that game and go with that. I don't think there's anything wrong with saying no if you need to (or if other members of your group need you to), but amazing things can happen when you say yes. Terrible, amazing things.
We're doing the Star Stone trial at the moment in Pathfinder, which is why my GM has asked I don't write up the sessions until we're back on Golarion (he's doing his own version and I think intends to run it for other people another time, so no spoilers!), but we created something so cool last session I have to tell you about it!
There's two important things that happened in the lead up: we acquired use of an airship and discovered our druid can reduce our transport time dramatically by portalling us through trees. Obvious next step? Get a really big pot, put a tree in it and have that on our airship. And awaken the tree - that can't go wrong, right? We sold it to the GM with the suggestion that the tree - a spruce pine - could grow into the ship, creating something akin to Moya in Farscape or the sea-going ships in Robin Hobb's Liveship Traders trilogy (which I haven't yet read but now really want to). The Star Stone trial can affect the magic, or something.
We helped the druid, all pouring in mythic chips. As the ritual ended, the tree stretched its limbs, needles extending. The balloon providing lift to the ship popped and for a few heart-stopping seconds we plummeted before the tree had converted enough of the ship and was able to return us to flight. Roots spread, wrapping through the timbers that made the ship - we could see the nutrients being sucked out and into the tree. The clean, worked wood was replaced by a mass of roots. The railings became old, gnarled wood. The trunk of the tree grew tall in place of a mast. A figure head grew from the prow, shuddered and shook, then looked back to us. The needles glowed, shimmering and shivering, as it spoke: "I am Yggdrisil".
Yggdrisil is a sentient airship sorceror (verdant bloodline). It is a magical plant, originally a spruce, so can photosynthesise and gets the rest of its nutrients from a ball of soil stored in the cargo area. It has some fire resistance, the ability to detect magic at will, an insatiable curiosity and a love of flight and freedom. Mental stats are all 18 (we took party averages to reflect the lifeforce we poured in in the form of mythic chips). If it likes you, your cabin will be spacious and accommodating to your needs - as a sorceror, it can use dancing lights to provide your lighting; as a living tree, it can extend part of itself as a shelf. If it doesn't like you, your bed will be gnarled and knotted and you may lose knickknacks you leave lying around.
I don't know its flight speed, precise spell list or its physical stats, but the imagery is so cool and I'm really excited by this. I'd love to use it in a novel, if I ever manage to focus long enough to write one.