My opponent has a Misthollow Griffin in exile. Can I cast it? By the time 601.2e checks to see if the proposed spell can legally be cast, the “You” in the Griffin's text will refer to me.

Edited Florian Horn (Feb. 9, 2016 03:28:02 PM)

No.

Since Misthollow Griffin is in exile, the “you” in its text refers to its owner, giving that player permission to cast it. You are not that player, and nothing is giving you permission to cast it. As such, as outlined in CR601.2 you cannot even begin to propose casting it in the first place.