58 cards where (the mana cost is greater than or equal to {C} or the text includes “{c},” or the text includes “{c}:” or the text matches the regex /pay \sm*\{c\}/ or the text includes “colorless mana was spent”)

Bearer of Silence (Oath of the Gatewatch #67)
Birthing Hulk (Oath of the Gatewatch #121)
Blinding Drone (Oath of the Gatewatch #41)
Breaker of Creation (Modern Horizons 3 #1)
Calamity of the Titans (Commander Masters #713)
Deceiver of Form (Oath of the Gatewatch #1)
Deepfathom Skulker (Oath of the Gatewatch #43)
Desecrate Reality (Commander Masters #714)
Devourer of Destiny (Modern Horizons 3 #2)
Dimensional Infiltrator (Oath of the Gatewatch #44)
Dread Defiler (Oath of the Gatewatch #68)
Echoes of Eternity (Modern Horizons 3 #4)
Eldrazi Confluence (Modern Horizons 3 Commander #32)
Eldrazi Displacer (Oath of the Gatewatch #13)
Eldrazi Linebreaker (Modern Horizons 3 #117)
Eldrazi Obligator (Oath of the Gatewatch #96)
Eldrazi Ravager (Modern Horizons 3 #5)
Eldritch Immunity (Modern Horizons 3 Commander #33)
Endbringer (Commander Masters #803)
Essence Depleter (Oath of the Gatewatch #69)
Flayer of Loyalties (Commander Masters #715)
Forsaken Monument (Commander Masters #950)
Glaring Fleshraker (Modern Horizons 3 #7)
Gravity Negator (Oath of the Gatewatch #45)
Havoc Sower (Oath of the Gatewatch #71)
Idol of False Gods (Modern Horizons 3 #210)
Immobilizer Eldrazi (Oath of the Gatewatch #97)
Inversion Behemoth (Modern Horizons 3 Commander #34)
It That Heralds the End (Modern Horizons 3 #9)
Kozilek's Command (Modern Horizons 3 Promos #11s)
Kozilek's Pathfinder (Oath of the Gatewatch #5)
Kozilek's Shrieker (Oath of the Gatewatch #73)
Kozilek, the Great Distortion (Commander Masters #2)
Matter Reshaper (Commander Masters #806)
Maw of Kozilek (Oath of the Gatewatch #99)
Mindmelter (Oath of the Gatewatch #149)
Mirrorpool (Commander Masters #1010)
Null Elemental Blast (Modern Horizons 3 #12)
Prophet of Distortion (Oath of the Gatewatch #46)
Reality Smasher (Oath of the Gatewatch #7)
Rise of the Eldrazi (Commander Masters #716)
Sea Gate Wreckage (Commander Masters #1028)
Selective Obliteration (Modern Horizons 3 Commander #35)
Slaughter Drone (Oath of the Gatewatch #79)
Snapping Voidcraw (Modern Horizons 3 #204)
Spatial Contortion (Commander Masters #809)
Spawn-Gang Commander (Modern Horizons 3 #140)
Stalking Drone (Oath of the Gatewatch #124)
Thief of Existence (Modern Horizons 3 #174)
Thought-Knot Seer (Oath of the Gatewatch #9)
Ulalek, Fused Atrocity (Modern Horizons 3 Commander #4)
Utter Insignificance (Modern Horizons 3 #78)
Vile Redeemer (Oath of the Gatewatch #125)
Walker of the Wastes (Oath of the Gatewatch #10)
Warping Wail (Commander Masters #812)
Wastescape Battlemage (Modern Horizons 3 #17)
World Breaker (Oath of the Gatewatch #126)
Zhulodok, Void Gorger (Commander Masters #704)

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