Okay, think I can have an idea here.....
Legendary Pokemon Capture Proposal
Since this place is still fairly ruin like, I propose its here that we can get Mew to be captured. You are leaving the temple, and walking a little far when ya see some twinkles in the distant grass. Ya start walking over only to realize ya seem to cant move to that grass through an invisible wall. You get confused, only for a hiker to ask, "Bud, why are you walking into a rock formation?" The player is just thoroughly confused, and thinks to ask if there is a sort of cave opening in the wall. The hiker says, "Yah, there is opening blocked by a bald man there. The fella keeps babbling on bout....stuff."
The player walks towards where the hiker points to, and doesn't see an old man, but a Mew. You walk up to talk to it, only for it to cry, and run away. The field of grass you see is all shimmering, and you end up having to play a game of cat and mouse in this grass field for mew ( which, can be finished easily if you recall the spot that twinkled originally cause that's where he'll be). Once found, ya battle and walla! Mew has been caught!
Upon capture, the Hiker is freaked out cause the cave he saw, just became a field of grass. He runs off a bit down the route in fright (if someone wants to, they can have him as a battle. I dont feel like it right now)
So ya, Mew in a game of Cat and Mouse with transforming the environment it lives in. Fun fun