Notably, Mulldrifter, Deathrite Shaman, and Ice-Fang Coatl all already have existing Secret Lair alternate versions, so the card selection's not even all that unique
Eventually, I realized that pretty much the universal source was the website (MPC)
Haunted Dead is the most efficient from a mana perspective when compared to jump-start cards like Radical Idea
Fellwar Stone, Nature's Lore, Three Visits, Skyshroud Elf, Bloom Tender, Faeburrow Elder, Chromatic Lantern, Coalition Relic, Wood Elves, Skyshroud Claim and Mirari's Wake can ramp and heavily fix your mana, taking the place of Gyre Sage, Solemn Simulacrum, Rampant Growth, Sakura-Tribe Elder and Xenagos, the Reveler - the latter is a win-more ramp, and his 2/2 token is not large enough to synergize with the power-based card draw, while the other four fix for a single color of mana (Ghired decks can sometimes be color-hungry), and this deck can't abuse the sad robot for value
Each of the five monocolor planeswalkers in Core Set 2021 has their own basic land featuring their home plane