Due to the banning of Paradox Engine in commander, Merchant Scroll was added in order to increase the chance of assembling the Dramatic Reversal and Isochron Scepter combo

First, I think you're running way too many lands. Even subtracting Maze of Ith and Glacial Chasm , you have 37 lands for producing mana. Urza's Power Plant , Urza's Mine and Urza's Tower are difficult to make work in EDH. As colorless sources, they're significantly worse than a basic Island when they aren't all in play; assembling them is difficult when they're each only one out of ninety-nine cards. I suggest cutting the Urza's lands, Darksteel Citadel and Seat of the Synod . They all die to Back to Basics , Magus of the Moon and Blood Moon , and the Citadel and Seat both get turned off by Stony Silence and Null Rod . (Though the artifact lands do boost Urza's Karn-friend, I think there're better ways to get artifacts out.) Thirty-two to thirty-three lands is probably about where you want to be; running enough mana rocks will help the deck move faster, and cutting lands means you draw better mid- and late-game too.

While we're talking about lands, it's great you're running Brainstorm , Ponder and Preordain . Ponder and Preordain are good in pretty much any blue list, but Brainstorm really goes from OK to busted with the help of shuffle effects. Fetches like Flooded Strand , Prismatic Vista or Polluted Delta are best, mainly because they don't have an ETB tapped to get in the way of your mana. Unfortunately, since these fetches are played in pretty much every format except Standard and Pauper, they're wildly expensive. Evolving Wilds and Terramorphic Expanse are on the table, as are Bad River and Flood Plain .

Tutors are excellent for making a deck more consistent; Fabricate and Merchant Scroll are great cards I see you're running. Whir of Invention is worth considering, and Muddle the Mixture finds both halves of the Isochron Scepter / Dramatic Reversal combo. Reshape and, if your rich AF, Transmute Artifact are also good. Instant-speed card-draw, from things like Fact or Fiction , Thirst for Knowledge or Glimmer of Genius , is a powerful effect.

Arcum's Astrolabe is worth considering. I haven't play-tested Urza, Lord High Artificer much more than a little, but having a one-mana artifact that cantrips and produces mana once Urza is out is probably a good effect, especially since you're already running all Snow-Covered Island s. Ramp like Chrome Mox , Mox Diamond and Mox Opal is expensive but extremely powerful; I'm having trouble determining your budget, mostly because you're running Mana Crypt , Mana Drain and Force of Will . Thought Vessel , Mind Stone , Prismatic Lens , Sky Diamond , Coldsteel Heart , Fellwar Stone and the soon-to-release Arcane Signet are all worth considering. In my experience, two-mana mana-rocks are vastly superior to three-mana mana-rocks, as they let you drop your general turn three rather than four.

There're a few artifacts-matter creatures you might want to consider. Vedalken Archmage is a real source of card-advantage, and Lodestone Golem is a great, sort-of one-sided sphere effect. Phyrexian Metamorph is a good way to copy stax pieces you want more of or mana rocks you want again, as are Copy Artifact and Sculpting Steel .

Consider Howling Mine . With Urza, High Lord Artificer is out, tapping it for mana on your turn results in it being a one-sided card-draw effect. Echo of Eons is good as a second Windfall -style card to go with your Narset, Parter of Veils . Sticking in one or two more infinite-mana combos is probably not a bad idea, either. Rings of Brighthearth with your Basalt Monolith or Power Artifact with a Grim Monolith or your Basalt Monolith can both produce an insta-win.

Good luck, man!