Overview

This deck is about flckering key value pieces that ETB to draw card(s), or remove pieces (reality acid being the best), or to untap pieces when they ETB (such as Basalt Monolith) to generate value. It's not quite at a cEDH level, but it's meant to be on the cusp - if EDH was ranked 1-10 and 9 & 10 were cEDH level, this would be an 8 (or so is the hope).
There's not a lot of ETB land fetch, as most of the white pieces that look for lands are 4 CMC or higher. Stuff like Kor Cartographer got cut for that very reason unfortunately - no point ramping with a 4cmc card, when the average deck CMC is 2.8 or so.
If you're wondering why I've got set symbols, it's because those are the cards I own and it's helping me figure out what I do and don't already have.

Deck Guide

This deck is lean. A relatively low average CMC (by my pods standards at least), so by turn 2 I hope to be be able to get interaction happening at some level.

This deck, despite being in blue with the potential for lots of great card draw, cards like Preordain, Serum Visions and Ponder got cut because it relies on recurring draw on ETB, so getting an engine up and running is really critical to keeping this deck moving forwards with any kind of explosive ability.

This deck has a decent chunk of it dedicated to removal, with 5 board wipes (do it after a Flicker from Yorion that makes your creatures safe until the end step), 5 counter spells and 5 pieces of ETB removal that you can flicker and keep getting value with.

Thassa's Win Con

Finding Thassa's Oracle

• The best way is to get recruiter of the guard to go find her (and also others like the en-Kor's and Cephalid)
• Muddle the Mixture can transmute to go find her.

Finding Jace, Wielder of Mysteries

Honestly, raw card draw is the only way to go find this planeswalker. But he's much harder to remove, and he can even draw the final card he needs to win the game with.

Library Goes Good Bye

There are two ways to get your library out once Thassa's Oracle is in your hand;

1. You have an Enlightened Tutor go find you Thought Lash. Cast Thought Lash. Then cast Thassa's Oracle, then with the oracle on the stack, pay 0 enough times and exile your library until you have 2 cards left. Then let the oracle resolve, your devotion is at 2 minimum so you win the game. Thought lash is resilient as it's a 1 card piece and an enchantment (so not a creature).
2. You assemble either Warrior en-Kor or Nomad en-Kor, as well as Cephalid Illusionist. Cast Thassa's Oracle, then with that on the stack, have an en-Kor pay 0 to target Cephalid, and Cephalid freaks out and mills you a card. And then you go to yourself "Hey, I can still afford to pay 0! Let's do that again! And again. And again ad nauseum style." Your library is now in the graveyard. Let Thassa's Oracle resolve, win game, go eat a sandwich or shuffle up for another game.

How to Exile when flickering with Fiend Hunter and Leonin Relic-Warder

Let's take Fiend Hunter, for example. Let's say you have a loop going with Felidar Guardian and Yorion. You just exiled Felidar Guardian and Fiend Hunter with Yorion's ETB, and you move to end step. These guys come back. Since they entered at the same time, you'll get to order how the enter the battle triggers will go onto the stack. Order with the Fiend Hunter exile on the bottom, and the felidar flicker on top. The flicker will resolve first, flickering out Yorion. Yorion comes back, then you flicker out the Felidar Guardian and Fiend Hunter. Then Fiend Hunter's exile resolves. Exile a creature. Then, since Fiend Hunter wasn't on the battlefield, that creature is just exiled. Forever. It's a weird ruling and they have now fixed this issue. You can also do the same trick with Leonin Relic-Warder as well.

Improving the Deck

• Drop Kiora Bests the Sea God for Cephalid Noble, which adds another layer of redundancy to the en-Kor strategy. Alternatively, another enchantment tutor like Idyllic Tutuor would be able to go find Thought Lash.
• Drop 2 cards (probably Kiora Bests the Sea God and another), then add in 2 more in a single category from: Flickerers, "Draw Cards, Best Part of Magic", Counter Spells, or Basic Lands.
• Drop the Thassa Wincon Engine section, add in Stasis, Winter Orb, Aven Mind Censor, and maybe Narset Parter of Veils for some stax. Take out the Kiora Bests the Sea God for some kind of win con like (Helm of Obedience & Rest in Peace) or (Painter's Servant & Grind Stone).
• Honestly, much of the stuff in the Tokens area could be worth running, and I kept it in there to give you guidance. The way I make a deck is I find about 200-300 cards then cull, so the maybe board is the first rejects. I did consider an etb lifegain deck where Flux Resoirvoir was a wincon, but I have since folded that into a much cheaper Brago deck (see here https://deckstats.net/decks/153823/1850039-brago-athenian-king-of-lifegai ).