Because, f*** it, Keranos is better than Assemble the Legion as a maindeck card. Not even close.
Planeswalkers:
4 Jace, Architect of Thought
1 Elspeth, Sun's Champion
Artifacts:
1 Elixir of Immortality
Enchantments:
2 Font of Fortunes
4 Detention Sphere
2 Banishing Light
1 Keranos, God of Storms
Instants:
2 Celestial Flare
2 Last Breath
2 Azorius Charm
1 Turn // Burn
2 Dissolve
2 Counterflux
4 Sphinx's Revelation
Sorceries:
4 Supreme Verdict
Lands:
4 Temple of Epiphany
4 Temple of Triumph
3 Temple of Enlightenment
4 Hallowed Fountain
2 Sacred Foundry
2 Steam Vents
4 Island
3 Plains
Sideboard:
1 Keranos, God of Storms
1 Assemble the Legion
2 Counterflux
2 Negate
2 Gainsay
1 Mizzium Mortars
1 Deicide
2 Nyx-Fleece Ram
1 Blind Obedience
1 Jace, Memory Adept
1 Reprisal
Also this basically plays like the UWb version of UW, where it plays 12 splash colour sources, with 8 temples, and then high enough impact cards to affect how its matchups play out. I don't feel like UW needs to have a removal buff (well, Turn // Burn is nice as an answer to Stormbreath and Obzedat, which splashing black can't do anyway) and that the toughest matchup outside of monsters is the mirror, where the Counterfluxes do serious work. Keranos gives the deck a better edge against Mono Black and the mirror, where unconditional removal becomes incredibly stressed. The choices of removal are generally to give the deck the best matchups in a broad sense, then sideboard for its worst matchups more heavily, namely monsters where the cards that come in are virtually integral to winning even if in small numbers.
I still think Monsters will be a bad matchup for this deck, but splashing Red I think makes this the best UW variant, giving it favourable matchups across the board, especially with the help UW already got from JOU.
Planeswalkers:
4 Jace, Architect of Thought
1 Elspeth, Sun's Champion
Artifacts:
1 Elixir of Immortality
Enchantments:
2 Font of Fortunes
4 Detention Sphere
2 Banishing Light
1 Keranos, God of Storms
Instants:
2 Celestial Flare
2 Last Breath
2 Azorius Charm
1 Turn // Burn
2 Dissolve
2 Counterflux
4 Sphinx's Revelation
Sorceries:
4 Supreme Verdict
Lands:
4 Temple of Epiphany
4 Temple of Triumph
3 Temple of Enlightenment
4 Hallowed Fountain
2 Sacred Foundry
2 Steam Vents
4 Island
3 Plains
Sideboard:
1 Keranos, God of Storms
1 Assemble the Legion
2 Counterflux
2 Negate
2 Gainsay
1 Mizzium Mortars
1 Deicide
2 Nyx-Fleece Ram
1 Blind Obedience
1 Jace, Memory Adept
1 Reprisal
Also this basically plays like the UWb version of UW, where it plays 12 splash colour sources, with 8 temples, and then high enough impact cards to affect how its matchups play out. I don't feel like UW needs to have a removal buff (well, Turn // Burn is nice as an answer to Stormbreath and Obzedat, which splashing black can't do anyway) and that the toughest matchup outside of monsters is the mirror, where the Counterfluxes do serious work. Keranos gives the deck a better edge against Mono Black and the mirror, where unconditional removal becomes incredibly stressed. The choices of removal are generally to give the deck the best matchups in a broad sense, then sideboard for its worst matchups more heavily, namely monsters where the cards that come in are virtually integral to winning even if in small numbers.
I still think Monsters will be a bad matchup for this deck, but splashing Red I think makes this the best UW variant, giving it favourable matchups across the board, especially with the help UW already got from JOU.