42 cards where the card is tagged “gains-flash”

A-Graveyard Shift (Streets of New Capenna #A-81)
Armor of Thorns (Vintage Masters #194)
Asinine Antics (Wilds of Eldraine #42)
Blast-Furnace Hellkite (The Brothers' War Commander #12)
Breaking Wave (Invasion #48)
Colossal Rattlewurm (Outlaws of Thunder Junction #159)
Crashing Tide (Rivals of Ixalan #34)
Dragon Grip (Khans of Tarkir #107)
Ghitu Fire (Invasion #144)
Grave Servitude (Mirage #126)
Graveyard Shift (Streets of New Capenna #81)
Harbinger of the Tides (Duel Decks: Merfolk vs. Goblins #7)
Hungering Yeti (Fate Reforged #105)
Lightning Reflexes (Dominaria Remastered #128)
Mutual Destruction (Ikoria: Lair of Behemoths #96)
Mystical Tether (Outlaws of Thunder Junction #19)
Mystic Veil (Visions #38)
Necromancy (Murders at Karlov Manor Commander #131)
Ninja (Unstable #61)
Oakshade Stalker // Moonlit Ambusher (Innistrad: Crimson Vow #212)
Oakshade Stalker // Moonlit Ambusher (Innistrad: Crimson Vow #212)
Parapet (Visions #14)
Patron of the Akki (Betrayers of Kamigawa #115)
Patron of the Kitsune (Betrayers of Kamigawa #19)
Patron of the Moon (Betrayers of Kamigawa #45)
Patron of the Nezumi (Commander Anthology Volume II #72)
Patron of the Orochi (Betrayers of Kamigawa #138)
Qasali Ambusher (Shards of Alara #184)
Relic Ward (Visions #16)
Rout (Commander 2021 #101)
Saproling Symbiosis (Dominaria Remastered #175)
Shove Aside (Alchemy: Murders at Karlov Manor #16)
Silver Scrutiny (Dominaria United #65)
Soar (Mirage #93)
Spider Climb (Visions #120)
Supernatural Rescue (Innistrad: Crimson Vow #37)
Swift Reckoning (Ultimate Masters #39)
Take for a Ride (Outlaws of Thunder Junction #148)
Tegwyll's Scouring (Wilds of Eldraine Commander #16)
Throat Wolf (Mystery Booster Playtest Cards 2021 #65)
Timely Ward (Commander Legends #363)
Twilight's Call (Duel Decks: Izzet vs. Golgari #76)
Ward of Lights (Mirage #47)

The message was clear to Sorin—time to search for something else.