Binge- Eating far too much and punishing everyone around you for it.
The concept of this deck is so simple, I'm surprised I've never seen a version of it before. Sheoldred, Bowmasters, and Narset punish opponent for trying to draw cards outside the drawstep. Day's Undoing is the epitome of drawing outside the drawstep. Cast Day's Undoing with any of the above, you win the game.
Day's + Sheoldred = 14 damage to the face, 14 life, a reloaded hand, and a deadly beater on the field
Days + Bowmasters = a 7/7 juggernaut and 7 damage clearing opponent's field/face along with a reloaded hand
Days + Narset = no hand for opponent, no grave for opponent, reloaded hand for you
Narset shuts down opponent from taking damage from Bowmasters or Shelodred, so if they are actually fielded at the same time they're a bit redundant, but at that point it won't matter, as you've got 7 cards and opponent will have nothing. In any of the above cases, it would take a miraculous series of draws to comeback, and most opponents will just scoop of any of the above combos go off.
The ideal turn sequence here is a turn 1 discard, turn 2 Bowmaster flash in, turn 3 Day's, and that's the ballgame. If you can't pull that off, you'll want at least 1 mana open for a counter or discard when you try for Day's, so the build runs 22 lands to help get to 4 when you need it.
The other good news is that the rest of the deck just says 'no' while fielding thrifty win conditions (even without the combo pieces in play), so if your Day's goes bust, you can always smash faces with Sheoldred or grind away with Bowmasters. I thought about running Psychic Frog as an alt win-con, but decided against it in favor of running more removal, as you want to keep a dead field so that when you pop off, opponent has nothing.
In addition, Day's is mainboarded grave hate (if inefficient), so that's a nice bonus. It does reset fetch lands, which is a pain, but it does so for both players, so that's a wash. Plus, you've got Urborg, so they might be swamps rather than dead draws/life draino.
The problem with the build is that countering Day's becomes opponent's only goal, so games 2 and 3 are fights over getting to/resolving Day's against potential counters. Since it's a 3-drop, that's aggravating, and since it's a sorcery, you can't use Force of Negation to defend it, but you absolutely will run into Force of Negation sideboarded. Plus, opponent will be ready with regular counter stuff, and you'll have to fight your way through it, which is a gigantic pain.
The first way around this is the eight 1-drop discard outlets the deck mainboards. A turn 1 discard pulls out opponent's response if you have the combo ready to go, or have a Day's and just want to dump your hand and reset. Mainboarding eight of them puts the math on your side, especially game 1. You've also got four mainboarded Spell Pierce against regular counter stuff and Spell Snare against Counterspell, and other threats like opponent's Bowmaster (which is a pain to play against obviously). I haven't build the sideboard yet, but it will have at least a few more answers for Force of Negation, as all this mainly cares about blasting off its combo.
Feedback appreciated.