I don't think Days Undoing actually does anything for the deck. I'd much rather have more fogs, which is the whole point of Days Undoing in the first place (when you're out of fogs to find some more, assuming you didn't
exile most when you treasure cruised). The deck also needed a better way to gain life which the prism rings allow you to do which come down much quicker than
Orbs of Warding. You might even want to play all 4 of the 3 mana
fog instead of 2 as well, but I wanted another pseudo-fog that cantripped which
Hydrolash does (and for all intents and purposes against agro it pretty much is
fog + draw). I'm not a big fan of the 5-6 mana spells that come down way later when you want their effect earlier in the game. If I have 5-8 mana, I'd much rather draw
Fascination than
Alhammarret's Archive.