Your search for "*monster of the abyss*" revealed the following:

Vivien, Monsters' Advocate (Promo Pack)
[Ikoria: Lair of Behemoths Promos]

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Goblin Attack Force
[BP02-EN008 Common]

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Dark Magician Girl
[MP24-EN009 Quarter Century Secret Rare]

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Ketria Triome
[Ikoria: Lair of Behemoths]

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Unchained Abomination
[MP20-EN175 Prismatic Secret Rare]

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Eye of Ojer Taq // Apex Observatory
[The Lost Caverns of Ixalan Commander]

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Blade Garoodia the Cubic Beast
[MVP1-EN034 Ultra Rare]

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Toon Ancient Gear Golem
[DLCS-EN073 Common]

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Knightmare Unicorn (Alternate Art)
[RA01-EN043 Platinum Secret Rare]

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Abaddon the Despoiler (171)
[Warhammer 40,000]

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Hitotsu-Me Giant
[LOB-002 Common]

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Merida - Wisp Conjurer (50/204)
[Attack of the Vine!]

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Fatal Abacus
[LOD-011 Rare]

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Kycoo the Ghost Destroyer
[BP02-EN011 Common]

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Two-Mouth Darkruler
[LOB-EN030 Common]

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Dark Magician the Knight of Dragon Magic
[BLMR-EN001 Secret Rare]

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