I'm a huge fan of the edition of Undying Evil.
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I play tested Crop Sigil. It works, but seems to be a half turn behind the Vessel. I'm not crazy about using either card, but maintain a play set of at least one enchantment to speed up the casting of Emrakul. The enchantments in the deck almost predominately for delirium only and the Vessel gets to the graveyard a tiny bit faster.
It's a little slow, but what are your thoughts on Nemisis Mask? Also, not sure what your'e thinking for your sacrifice engine, but Bone Splinters came to mind as possible removal that has no disadvantage here.
I understand the addition of the Latchkey and where it contributes, but it would seem to me that it runs the risk of delaying the deck a turn and opening up for an easier response from your opponent.