I'm fine with either, honestly. I like the "fly" plan more - in that it's more creative - but a "quick" (we know that it won't be) combat with a dino would be fine. Though if you want to go for that option, I think we should just say that ALL the Chwingas turn into a Dino (or that they turn Weed into one) so that we don't have too many creatures on the map. (It's just easier on me).
The chwingas can only turn themselves into cr 1/4. They would turn the PCs into dinos because we can turn into cr 6 creatures.
The chwingas are much more valuable using their spell abilities.
1 has already cast polymorph
3 (or 4 if we include weed) would polymorph us and then stay hidden and maintain concentration from the key room.
The other 4 would support with spells. (Dispel magic, confusion, fairy fire).
The advantage of us all being a Dino is we don’t take any actual damage if we get hit because we use the HP of the Dino form. No one uses any resources.
So, in that respect, if you think we’d win handedly, you could hand-waive and narrate the whole combat and move us on.
I do love the idea of turning Weed into a Dino! The rest of us will be flies, but the last 4 have to combine their abilities to turn weed into something more powerful
Fly in and attack and then weed joins us as a Dino. The rest of the Chwingas will just hide.