15 cards where the lore includes “jellyfish”

Avizoa (Weatherlight #35)
Clinging Anemones (Gatecrash #31)
Dormant Gomazoa (Rise of the Eldrazi #62)
Esperzoa (Double Masters #49)
Flumph (Adventures in the Forgotten Realms #15)
Glimmerbell (Ikoria: Lair of Behemoths #53)
Glowing Anemone (Mercadian Masques #81)
Gluntch, the Bestower (Commander Legends: Battle for Baldur's Gate #275)
Gomazoa (Commander 2011 #48)
Guard Gomazoa (Planechase Anthology #17)
Hydroid Krasis (Ravnica: Clue Edition #195)
Man-o'-War (Dominaria Remastered #58)
Numbing Jellyfish (Unstable #42)
The Reality Chip (Kamigawa: Neon Dynasty #74)
Watchful Blisterzoa (Phyrexia: All Will Be One #78)

Though this query has ended, its relics still slumber in New Argive.