Very interesting build. Several questions about your choices.
Merrow Reejerey - does it work well for you? I found him rather CMC-wise expensive and his second ability doesn't help much since ideally we should use Vials to bring more folks. So I took Reejerey completely off my deck.
Standstill - I'm still unsure about this card. Basically, instead of moving forward, it can hamper us. Especially when we don't have any Vials on the table and the opponent plays some slow combo. Have you tried
Saprazzan Heir? I understand that she is easily killable and doesn't provide an immediate result, but can serve as an unblocable runner for a while.
Mishra's Factory - very interesting idea. This land looks very powerful and works well together with
Mutavault. Perhaps, will try 4 of these in my deck to be more aggressive and improve mana base. I currently run 19 lands with 4 Mutavaults and 2 Caverns of Souls and this is not enough.
Cavern of Souls are not very helpful and I was thinking about adding
Wasteland, but Factories look like a better option for an aggressive deck.