I am sure I will give up at some point on account of the $25 per set cost or the prize of some of the more expensive cards, but IF I was to go for four redemptions of the Theros block (that's twelve redemptions total... ouch!) this is what I am currently missing.
For Theros
For BNG:
For NYX:
[February 1, 2015] And because opening packs for the sake of Mythic Rares is strictly worse than buying lottery tickets, here are the prices for cards $1 plus, highlighting the non Mythic Rares.