Daywalker- Day's Undoing + Narset (a planeswalker)
The theory is simple. Day's Undoing resets your ammo, and if you cast it with Narset on the field, you've robbed opponent of all cards in hand while you have a full 7 cards. If that combo goes off, its GG. Even if you don't have Narset, Day resets the grave and hand, and doesn't really hurt you as you're gunna be moving through the deck relatively quickly, can dump your cheap spells before casting Day, and can catch opponent with unused ammo. To top it all off, Day resets the grave, so it hurts everything that needs a full grave, which is quite a bit in modern, so this build functions as a semi-mainboarded anti-meta without hurting itself. Sorry Murktide.
The rest of the deck either keeps you alive or grinds for the win condition. Your win conditions are:
Brazen Borrower damage
Hall of Storm Giants damage
Jace ult abil
Synergy breakdown as follows:
Borrower: preserves material and tempo, good win condition clock (7 turns on its own), and best of all, can store itself for later use, which works PERFECTLY with Day's Undoing, as you can store it then play Day, get a new hand, and have Borrower ready to go for later when you need it. The bounce abil is also mainboard hate agianst Murktide and Hammertime, as bouncing Murk/equipped critter/hammer makes Murk/the hammer basically useless.
Hard Evidence: helps fix blue's weakness against fast critters, replaces itself, preserves tempo, counter target Ragavan. You can even dump it, store the clue, then cast Day for more tempo and material savings.
Prismatic Ending: easy access to all 5 colors makes it ideal removal. Fetch lands + Triome's and the pain lands put this card over the top while keeping the dead drops to a minimum.
Path to Exile: opponent hopefully won't be able to use the extra land as well, cause you'll nuke his hand and grave hopefully, so its really just a 1-drop free removal a good portion of the time. And since Day shuffles your grave back in, you get to keep reusing them.
An Offer You Can't Refuse: same logic as Path, opponent can't use the extra mana with no cards. You need Day to pop off without interference, and this helps that happen for cheap, and potentially no downside.
Land Count: only problem with this build is it needs to hit 3 lands as fast as possible, and needs to have open ammo available to protect Narset and/or pop off Day. So, higher land count helps you get to your 3 lands quickly and with consistency. The extra lands are all tech lands/fetch lands/win conditions, all of which synergize perfectly with the rest of the build. If you topdeck one of the seven draw lands and you don't need it, no problem. Effectively meaning this deck is only running 16 'dead' lands (not counting the win condition/otwara lands), which means you're not going to be topdecking useless lands much. When/if you pop off the Day combo, a higher land count also means you'll be able to take advantage of the high material count by developing quickly with land drops for the next few turns with consistency.