36 cards where the illustration contains “back-to-back”

Arachnogenesis (Commander Masters #647)
Avacynian Missionaries // Lunarch Inquisitors (Shadows over Innistrad #6)
Avacynian Missionaries // Lunarch Inquisitors (Shadows over Innistrad #6)
Blessed Alliance (Eldritch Moon #13)
Boon Reflection (Double Masters #10)
Brought Back (Core Set 2020 #9)
Carven Caryatid (Ravnica: City of Guilds #155)
Ceaseless Searblades (Lorwyn #158)
Clever Combo (Unstable #105)
Collective Brutality (Eldritch Moon #85)
Contractual Safeguard (New Capenna Commander #115)
Defense of the Heart (Wilds of Eldraine: Enchanting Tales #80)
Emrakul's Influence (Eldritch Moon #157)
Energy Flux (Antiquities #9)
Goblin Chainwhirler (Dominaria #129)
Harsh Mercy (Onslaught #39)
Harvestguard Alseids (Journey into Nyx #13)
Icatian Javelineers (Fallen Empires #8c)
Jace, Mirror Mage (Zendikar Rising #63)
Jenny Flint (Doctor Who #741)
Join Forces (Dominaria United #21)
Keen Duelist (Commander 2021 #42)
Limited Resources (Exodus #10)
Madame Vastra (Doctor Who #747)
Mirage Phalanx (Crimson Vow Commander #73)
Order of the Sacred Bell (Champions of Kamigawa #232)
Paired Tactician (Zendikar Rising #31)
Parallel Lives (Wilds of Eldraine: Enchanting Tales #83)
Pay Tribute to Me (Archenemy: Nicol Bolas Schemes #14★)
Rowan Kenrith (Battlebond #2)
Sunshot Militia (The Lost Caverns of Ixalan #168)
Swelter (Judgment #101)
The Royal Scions (Throne of Eldraine #199)
Thrill of Possibility (Phyrexia: All Will Be One #151)
Triton Tactics (Theros #71)
Valor in Akros (Masters 25 #38)
Woodcaller Automaton (The Brothers' War #377)

This search is finished. Now the real work can begin.