This is a rebuild and combination of 2 decks I owned and made at the same time, a high level Thassa's-Oracle combo Yorion deck, and a (then-budget) Lifegain Brago deck (which won by beating in faces with unblockable Serra Avatars). https://deckstats.net/decks/153823/1850039-brago-king-of-lifegain-via-ost

This is more traditional approach to Brago. It aims to resolve infinite turns in a row, or make infinite mana and win from there. To win, the key pieces are an extra turn spell (such as time warp), then either flickering Archaeomancer or Mnemonic Wall which returns the extra spell card from the graveyard to your hand. Flickering can be done with Brago, Isochron Sceptre imprinted with a flicker instant, or Crystal Shard.

Alternatively, Strionic Resonator/ Lithoform Engine can make infinite ETBs with a Brago activation and at least 2 mana from mana rocks (such as Sol Ring), 3 or more mana makes infinite mana in your combat step (so need another value piece or wheels just spin).

From the original Yorion Deck

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 ).

Original Maybeboard

1 Augury Owl
1 Austere Command
1 Aven Battle Priest
1 Banisher Priest
1 Banishing Light
1 Barrin, Tolarian Archmage
1 Bishop of Wings
1 Blazing Archon
1 Blind Obedience
1 Blue Sun's Zenith
1 Brightmare
1 Bruna, Light of Alabaster
1 Bulwark Giant
1 Call for Unity
1 Cast Out
1 Cataclysmic Gearhulk
1 Cathedral Sanctifier
1 Cephalid Aristocrat
1 Chain of Vapor
1 Cloudkin Seer
1 Commander's Sphere
1 Countless Gears Renegade
1 Courier Griffin
1 Cryptic Command
1 Day of Judgment
1 Dragonlord Ojutai
1 Drannith Magistrate
1 Elite Guardmage
1 Elixir of Immortality
1 Ephara, God of the Polis
1 Familiar's Ruse
1 Felidar Sovereign
1 Flickerwisp
1 Generous Gift
1 Gift of Estates
1 Glimmerpoint Stag
1 Harmonious Archon
1 Highcliff Felidar
1 Hour of Revelation
1 Jace, the Mind Sculptor
1 Jin-Gitaxias, Core Augur
1 Karmic Guide
1 Marble Diamond
1 Meteor Golem
1 Mnemonic Wall
1 Moorland Haunt
1 Mox Tantalite
1 Naru Meha, Master Wizard
1 Oath of Teferi
1 Ornitharch
1 Palace Jailer
1 Ponder
1 Rambunctious Mutt
1 Rest in Peace
1 Restoration Angel
1 Return to Dust
1 Reveillark
1 River's Rebuke
1 Silent Sentinel
1 Sky Diamond
1 Skyclave Apparition
1 Spine of Ish Sah
1 Stasis
1 Sun Titan
1 Supreme Verdict
1 Teferi's Time Twist
1 Teferi, Hero of Dominaria
1 Teferi, Time Raveler
1 Telepathy
1 Thran Dynamo
1 Tidal Barracuda
1 Venser, Shaper Savant
1 Venser, the Sojourner
1 Watcher for Tomorrow
1 Winter Orb