34 cards where the full Oracle text includes “its mutate cost,”

Archipelagore (Ikoria: Lair of Behemoths #41)
Auspicious Starrix (Ikoria: Lair of Behemoths #144)
Boneyard Lurker (Ikoria: Lair of Behemoths #178)
Brokkos, Apex of Forever (Ikoria: Lair of Behemoths #179)
Cavern Whisperer (Ikoria: Lair of Behemoths #79)
Chittering Harvester (Ikoria: Lair of Behemoths #80)
Cloudpiercer (Ikoria: Lair of Behemoths #112)
Cubwarden (Ikoria: Lair of Behemoths #7)
Dirge Bat (Ikoria: Lair of Behemoths #84)
Dreamtail Heron (Ikoria: Lair of Behemoths #47)
Everquill Phoenix (March of the Machine Commander #275)
Gemrazer (Ikoria: Lair of Behemoths #155)
Glowstone Recluse (Ikoria: Lair of Behemoths #156)
Huntmaster Liger (Ikoria: Lair of Behemoths #16)
Illuna, Apex of Wishes (Dominaria United Commander #154)
Insatiable Hemophage (Ikoria: Lair of Behemoths #93)
Lore Drakkis (Ikoria: Lair of Behemoths #194)
Majestic Auricorn (Ikoria: Lair of Behemoths #22)
Migratory Greathorn (Ikoria: Lair of Behemoths #165)
Mindleecher (Commander 2020 #44)
Necropanther (Ikoria: Lair of Behemoths #196)
Nethroi, Apex of Death (Dominaria United Commander #163)
Otrimi, the Ever-Playful (Commander 2020 #12)
Parcelbeast (Ikoria: Lair of Behemoths #199)
Porcuparrot (Ikoria: Lair of Behemoths #128)
Pouncing Shoreshark (Ikoria: Lair of Behemoths #64)
Regal Leosaur (Ikoria: Lair of Behemoths #202)
Sawtusk Demolisher (Commander 2020 #64)
Sea-Dasher Octopus (Ikoria: Lair of Behemoths #66)
Snapdax, Apex of the Hunt (Ikoria: Lair of Behemoths #209)
Souvenir Snatcher (Commander 2020 #38)
Trumpeting Gnarr (Ikoria: Lair of Behemoths #213)
Vadrok, Apex of Thunder (Ikoria: Lair of Behemoths #214)
Vulpikeet (Ikoria: Lair of Behemoths #37)

This search is finished. Now the real work can begin.