38 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\}/)

Bearer of Silence (Oath of the Gatewatch #67)
Birthing Hulk (Oath of the Gatewatch #121)
Blinding Drone (Oath of the Gatewatch #41)
Calamity of the Titans (Commander Masters #713)
Deceiver of Form (Oath of the Gatewatch #1)
Deepfathom Skulker (Oath of the Gatewatch #43)
Dimensional Infiltrator (Oath of the Gatewatch #44)
Dread Defiler (Oath of the Gatewatch #68)
Eldrazi Displacer (Oath of the Gatewatch #13)
Eldrazi Obligator (Oath of the Gatewatch #96)
Endbringer (Commander Masters #803)
Essence Depleter (Oath of the Gatewatch #69)
Flayer of Loyalties (Commander Masters #715)
Forsaken Monument (Commander Masters #950)
Gravity Negator (Oath of the Gatewatch #45)
Havoc Sower (Oath of the Gatewatch #71)
Immobilizer Eldrazi (Oath of the Gatewatch #97)
It That Heralds the End (Modern Horizons 3 #9)
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)
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)
Slaughter Drone (Oath of the Gatewatch #79)
Spatial Contortion (Commander Masters #809)
Stalking Drone (Oath of the Gatewatch #124)
Thought-Knot Seer (Oath of the Gatewatch #9)
Vile Redeemer (Oath of the Gatewatch #125)
Walker of the Wastes (Oath of the Gatewatch #10)
Warping Wail (Commander Masters #812)
World Breaker (Oath of the Gatewatch #126)
Zhulodok, Void Gorger (Commander Masters #704)

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