41 cards where the card types include “merfolk” and the card types include “legend”

Adrix and Nev, Twincasters (Murders at Karlov Manor Commander #198)
Alandra, Sky Dreamer (Murders at Karlov Manor Commander #94)
Ambassador Laquatus (Tenth Edition #65)
Araumi of the Dead Tide (Commander Legends #267)
A-Tatyova, Steward of Tides (Dominaria United #A-222)
Attuma, Atlantean Warlord (Marvel Super Heroes #47)
Dalakos, Crafter of Wonders (Theros Beyond Death #212)
Emperor Mihail II (The Lost Caverns of Ixalan Commander #155)
Empress Galina (Invasion #54)
Emry, Lurker of the Loch (Edge of Eternities Commander #71)
Fluros of Myra's Marvels (Unfinity #46)
Hakbal of the Surging Soul (The Lost Caverns of Ixalan Commander #3)
Jori En, Ruin Diver (Duel Decks: Mind vs. Might #23)
Kenessos, Priest of Thassa (Jumpstart 2022 #13)
Kiora, Sovereign of the Deep (March of the Machine: The Aftermath #35)
Kiora, the Rising Tide (Foundations #45)
Kopala, Warden of Waves (The Lost Caverns of Ixalan Commander #160)
Kumena, Tyrant of Orazca (The Lost Caverns of Ixalan Commander #274)
Namor the Sub-Mariner (Marvel Super Heroes #69)
Neerdiv, Devious Diver (Foundations Jumpstart #36)
Nev, the Practical Dean (Secrets of Strixhaven Commander #41)
Nicanzil, Current Conductor (The Lost Caverns of Ixalan #236)
Noyan Dar, Roil Shaper (Battle for Zendikar #216)
Orysa, Tide Choreographer (Secrets of Strixhaven #62)
Prime Speaker Zegana (Foundations #664)
Sharae of Numbing Depths (Wilds of Eldraine #213)
Svyelun of Sea and Sky (The Lost Caverns of Ixalan Commander #175)
Sygg, River Cutthroat (Zendikar Rising Commander #103)
Sygg, River Guide (Lorwyn #251)
Sygg, Wanderwine Wisdom // Sygg, Wanderbrine Shield (Lorwyn Eclipsed #76)
Sygg, Wanderwine Wisdom // Sygg, Wanderbrine Shield (Lorwyn Eclipsed #76)
Talrand, Sky Summoner (Outlaws of Thunder Junction Commander #116)
Tatyova, Benthic Druid (Foundations #247)
Tatyova, Steward of Tides (Dominaria United #222)
Thada Adel, Acquisitor (Worldwake #40)
Thrasios, Triton Hero (Commander 2016 #46)
Tishana, Voice of Thunder (The Lost Caverns of Ixalan Commander #291)
Tuvasa the Sunlit (Commander 2018 #47)
Vohar, Vodalian Desecrator (Dominaria United #226)
Vorel of the Hull Clade (The Lost Caverns of Ixalan Commander #294)
Zareth San, the Trickster (Zendikar Rising #242)
Zegana, Utopian Speaker (The Lost Caverns of Ixalan Commander #298)

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