Hi! I think as many players trying to do (regular) shaymin quest there's a bug in the script which is in the last part of quest when you try to interact the oblelisk nothing happen when you must be taken to shaymin .
Note: I have well done the quest i have all the pokemon that you need for quest ( Arcanine - Pokemon with chlorophyll (ability) and leech seed (move) - Pokemon with serene grace (ability) and roost (move) - Pokemon with natural cure (ability) - Pokemon with 252 EV defense - Pokemon with 31 IV speed )
Thanks and sorry for my bad english :p