Arceus Flying's a prett poor Marsh check since it drops to HP Ice or Rock Tomb with a bit of prior damage. A more reliable check would be Arceus-Poison.
As for a question of my own, this is the 4th time in a row that I've encountered a Tapu Lele psychic spam team. Is there a particular reason for that, or just bad luck? All of them consisted of Smeargle to lay webs and rocks, Lele to set terrain, Deoxys and Mewtwo-Y to abuse it, with the last two pokemon changing depending on the team. Every single time I played against it I just got steamrolled. What would you say is the best counter to this strategy?
EDIT: WTF? I JUST encountered another one. Pls help my elo is dropping fast.