Normally, I like to go through each card, and note upsides and downsides. That'll be a lot of text in a deck this big though, so I'll go through subsections instead.
Battle of Wits
This is the pile that inspired this deck. 3 BoW in the main, plus one in the side as a Granted target. One Moon-Blessed Cleric acts as an Eladamri's Call tutor for the Bow. I'm not running 4 because it's a fairly dead card otherwise and I don't want to see it naturally.
Card Advantage
This section pretty much consists of everything that draws a card.
- Abundant Growth replaces itself while fixing mana
- Bloodbraid is a hasty threat that digs for another card; most likely to be removal
- Bonecrusher is two cards in one (Why did WotC let this mechanic through?)
- EI looks at three cards
- Ice taps something down while replacing itself
- Manamorphose replaces itself while fixing mana
- Omnath draws a card on etb, replacing itself. Also turns lands into life. And mana. And free damage.
- Ragavan steals cards from the opponent and lets us cast it, effectively drawing us a card from the opponent's deck.
- Risen Reef 'draws' upon entering the battlefield, and replaces any other elementals we happen to cast
- Spreading Seas replaces itself and neutralizes an opposing land
- T3feri draws cards while returning opponent's cards to hand, and prevents their instant interaction
Domain
These cards reward a greedy mana base. Leyline Binding and Prismatic Ending are prime removal, Tribal Flames and Kavu deal large chunks of damage, and Bring to Light enables a small toolbox plan.
I know not all of these are technically 'Domain'. However, since Ending and Bring to Light care about colors, in this list they basically have Domain.
Elementals
Elementals have gained a reputation with MH2 for being quite strong, and with good reason. Free removal is always nice. Risen Reef provides mountains of card advantage, and Ephemerate and Cloudshift provide let us double up on evoke triggers while saving the creatures. Omnath does some beastly (elementally?) things if not removed quickly.
Lands
Consists of lands ¯_(ツ)_/¯
Madcap
This was a fairly standard package across dozens of BoW decks I looked at. We lose cards like Esper Sentinel and Scion of Draco, but this drops a massive threat that the opponent must answer quickly. This is probably the most flexible package though, as some metas will want Esper Sentinels and Scions over a clunky artifact creature.
Mana Fixing
These make our mana smoother and thus the quality of life better. I'm running Ignoble over Noble because Ignoble makes , which is the most important colors, and are our least important.
Protection
These mostly hate out specific strategies while proving us with powerful cards. Force is the only counterspell in the list, so probably worth hanging on to for the more powerful cards
Removal
52 of some of the best removal spells modern has to offer. There's no such thing as overkill. For reference I'll sort them by speed and effect.
Spreading Seas is interesting. It is removal in the sense that it removes something, but it just removes type and text. Most relevant against Urza's Saga, Inkmoth Nexus, Den of the Bugbear, Hall of Storm Giants, and Celestial Colonnade. However as it makes lands Islands it can shut out non blue strategies, and will incidentally make Utopia Sprawl fall off.
Toolbox
This is another highly customizable subsection. I included Supreme Verdict for creature heavy decks and Scapeshift + Valakuts as an alt win con. For Eladamri's Call toolboxers I have Collector Ouphe for artifacts and Cleric to tutor Battle of Wits. However, both can grab powerful cards from other sections as needed (ie Madcap Experiment or Solitude respectively).
Wishboard
As we are running a 250 card deck, we can sideboard in four copies of a card and easily never see them. So instead we have a wishboard plan.
The wishboard consists of
- removal (Detention Sphere, Firespout, Force of Vigor, Fracturing Gust, Rip Apart, Wear / Tear)
- hate cards (Dryad Militant, Klothys, Lavinia, Unmoored Ego, Vexing Shusher)
- beaters (Geist of Saint Traft, Kitchen Finks)
Also have Battle of Wits to wish as a game win and Emrakul as an anti mill card (this is a flex slot, Emmy will probably actually never be relevant)
Tarmogoyf
Goyf doesn't really fit in with any of the other sections, but it can be a massive creature early in the game. If WotC prints something new and broken Goyf (or Bloodbraid Elf) probably gets cut.