31 cards where it’s legal in Standard and the text includes “this spell” and the text includes “less to cast” and the mana value >= 5

Angelic Observer (Streets of New Capenna #1)
Argivian Phalanx (Dominaria United #5)
Cactarantula (Outlaws of Thunder Junction #158)
Capricious Hellraiser (Phyrexia: All Will Be One #125)
Cinderslash Ravager (Phyrexia: All Will Be One #200)
Death-Rattle Oni (March of the Machine: The Aftermath #13)
Diregraf Rebirth (Innistrad: Midnight Hunt #220)
Explosive Singularity (Kamigawa: Neon Dynasty #140)
Gargantuan Leech (The Lost Caverns of Ixalan #107)
Hamlet Glutton (Wilds of Eldraine #173)
Hearth Elemental // Stoke Genius (Wilds of Eldraine #136)
Hollow Marauder (Outlaws of Thunder Junction #90)
Leyline Binding (Dominaria United #24)
Molten Monstrosity (Dominaria United #139)
No One Left Behind (The Brothers' War #109)
Overwhelming Remorse (The Brothers' War #110)
Quicksand Whirlpool (The Lost Caverns of Ixalan #31)
Reality Heist (Kamigawa: Neon Dynasty #75)
Rowdy Research (Wilds of Eldraine #312)
Shadow of Mortality (Streets of New Capenna #94)
Sky-Blessed Samurai (Kamigawa: Neon Dynasty #37)
Suspicious Detonation (Murders at Karlov Manor #145)
The Pride of Hull Clade (Murders at Karlov Manor #172)
The Skullspore Nexus (The Lost Caverns of Ixalan #212)
This Town Ain't Big Enough (Outlaws of Thunder Junction #74)
Tolarian Terror (Dominaria United #72)
Vanquish the Horde (Innistrad: Midnight Hunt #41)
Walking Skyscraper (Kamigawa: Neon Dynasty #263)
Wolfkin Outcast // Wedding Crasher (Innistrad: Crimson Vow #229)
Wolfkin Outcast // Wedding Crasher (Innistrad: Crimson Vow #229)
Writhing Necromass (Dominaria United #115)
Yavimaya Sojourner (Dominaria United #191)

Their mind whirled with grand plans, never thinking of what might happen if they got to the end of the list.