You need graveyard hate (most loops use resources from there) and land interaction and, ideally, ways to stop your opponent from playing Lumra
If you want, you can use avatar #1 for Deck A, and a different avatar #2 for Deck B, and have a different avatar for each one of your decks
The world of artifact-based card draw expanded as Wizards becomesbecame more comfortable printing artifacts with colors, but it doesnt change the simple fact that artifacts are busted, especially once you chuck in card advantage
Our options are therefore as follows: Azorius v Jund: Will, Scion of Peace & Ikra Shidiqi, the Usurper + Kediss, Emberclaw Familiar Rakdos v Bant: Judith, Carnage Connoisseur & Shanna, Purifying Blade Selesnya v Grixis: Trelasarra, Moon Dancer & Solkanar the Swamp King Boros v Sultai: Firesong and Sunspeaker & Zimone and Dina Golgari v Jeskai: Beledros Witherbloom & The Archimandrite Okay, there should be six, but if you can find an oppositional pair in Dimir and Naya that can both be reasonably called a life gain deck, go for it
Choosing Our Commander There's three potential commanders to lead the deck: the new face commander Sliver Gravemother, the other new option Rukarumel, Biologist, and the reprint option Sliver Hivelord
This is the kind of thing where I was in the room as the teams were coming up with these solutions