I don’t fully understand why this card is mythic.
It’s a story driven card, and I suppose this was really to promote what exactly is happening to the characters during their stay on Amonkhet. I just don’t think that should translate to mythic status. The effect doesn’t really feel mythic either. I believe there’s been some Curses in the past that have had much better effects on the game – and weren’t mythic or had an unreasonable casting cost. See Curse of Death’s Hold.
I don’t want to write this card off completely – this may be an out of the box technology against heavy control lists. The clock is quick enough that resolving this would close up a game quickly. I doubt it’s odds, and with much of the community ready to adopt Cast Out from Amonkhet – the prospects of this card are slim to none at best.
I don’t believe there will be much desire for this card. Even outside of Constructed this won’t be a high priority for Commander/Casual players unless it’s strictly to use story element cards. As a story card, it’s successful – but even singing that praise won’t have significant impact on this card’s value. There’s little reason to acquire this card early on, and expect players not to do so.