37 cards where the illustration contains “sea-weed”

Benthicore (Lorwyn #53)
Bident of Thassa (The Brothers' War Commander #80)
Brine Giant (Theros Beyond Death #44)
Control Win Condition (Mystery Booster Playtest Cards 2019 #19)
Dakra Mystic (Journey into Nyx #35)
Dive Down (Ixalan #53)
Dream Tides (Visions #31)
Drowned (The Dark #24)
Drown in the Loch (Secret Lair Drop #270)
Excavation (Prophecy #33)
Forest (RNA Ravnica Weekend #B09)
Gudul Lurker (Dragons of Tarkir #56)
Island (Dominaria #256)
Kiora, the Tide's Fury (Jumpstart: Historic Horizons #10)
Maeve, Insidious Singer (Game Night: Free-for-All #2)
Mantle of Tides (Throne of Eldraine #52)
Merfolk Secretkeeper // Venture Deeper (Throne of Eldraine #53)
Merseine (Fallen Empires #23b)
Mystic Reflection (Kaldheim #69)
Nyxborn Triton (Born of the Gods #46)
Octoprophet (Core Set 2020 #70)
Reap the Seagraf (Dark Ascension #72)
Retreat to Coralhelm (Secret Lair Drop #407)
Saprazzan Heir (Mercadian Masques #99)
Seafloor Stalker (Zendikar Rising #78)
Sea Scryer (Mirage #90)
Seasinger (Fallen Empires #25)
Sea Troll (Homelands #39)
Simic Guildgate (Ravnica Allegiance #258)
Sunken Ruins (Zendikar Expeditions #27)
Surge Mare (Core Set 2019 #77)
Svyelunite Temple (Fallen Empires #102)
Tangle Kelp (The Dark #37)
Tatyova, Steward of Tides (Dominaria United #222)
Teferi's Wavecaster (Core Set 2021 #327)
Tidal Barracuda (Commander 2020 #39)
Volshe Tideturner (Dominaria United #77)

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