Svella:

• Highland Weald -> Highland Forest
• Beast Within? Temple of the False God? Rogue's Passage? Rhythm of the Wild?

Harald:

• Eyeblight Massacre -> Heritage Druid
• Elvish Guidance?
• Lightning Greaves?

Araumi:

• Swamp -> Malakir Rebirth
• Stitcher's Supplier? Millikin? Port of Karfell? Talisman of Dominance?
• Tribute Mage? Corpse Connoisseur? Notion Rain? Impaler Shrike?

Mutate

Auspicious Starrix - Elk Beast - Mutate 5G -> 5 Permanents

Gemrazer - Beast - Mutate 1GG -> Destroy 3 Artifacts/Enchantments

Migratory Greathorn - Beast - Mutate 2G -> 3 basics

Sawtusk Demolisher - Beast - Mutate 3G -> 3 Beast Within

Souvenir Snatcher - Bird - Mutate 5U -> Steal 3 noncreature artifacts

Dreamtail Heron - Elemental Bird - Mutate 3U -> 3 Cards

Other

Ongoing investigation!

Additions:
Soldevi Adnate (mana dork)
Basal Thrull (mana dork)
Whisper, Blood Liturgist (sacc outlet, recursion)
Skyscanner (card draw)
Abyssal Gatekeeper (removal?)
Worn Powerstone
Apprentice Necromancer
Leaden Myr

Interestting list: https://tappedout.net/mtg-decks/shirei-peasant/

Possible additions:

Archfiend of Ifnir
Ertai, the Corrupted
Overcharged Amalgam
Teferi, Master of Time
Linvala, Shield of Sea Gate
Burning Rune Demon
Nezahal, Primal Tide
Phyrexian Tower
Reveillark
Street Wraith
Toxrill, the Corrosive
Nephalia Drownyard
Cephalid Coliseum

Organ Hoarder

Moon-Blessed Cleric

Oriq Loremage
Thought Courier
Jace's Archivist
Thousand-Year Elixir

Loyal Warhound
Knight of the White Orchid