28 cards where the mana cost is greater than or equal to {C}

Breaker of Creation (Modern Horizons 3 #1)
Calamity of the Titans (Commander Masters #713)
Deceiver of Form (Oath of the Gatewatch #1)
Devourer of Destiny (Modern Horizons 3 #2)
Echoes of Eternity (Modern Horizons 3 #4)
Eldrazi Confluence (Modern Horizons 3 Commander #32)
Eldrazi Linebreaker (Modern Horizons 3 #117)
Eldrazi Ravager (Modern Horizons 3 #5)
Eldritch Immunity (Modern Horizons 3 Commander #33)
Endbringer (Commander Masters #803)
Flayer of Loyalties (Commander Masters #715)
Glaring Fleshraker (Modern Horizons 3 #7)
Inversion Behemoth (Modern Horizons 3 Commander #34)
It That Heralds the End (Modern Horizons 3 #9)
Kozilek's Command (Modern Horizons 3 #11)
Kozilek, the Great Distortion (Commander Masters #2)
Matter Reshaper (Commander Masters #806)
Null Elemental Blast (Modern Horizons 3 #12)
Reality Smasher (Oath of the Gatewatch #7)
Rise of the Eldrazi (Commander Masters #716)
Selective Obliteration (Modern Horizons 3 Commander #35)
Spatial Contortion (Commander Masters #809)
Thief of Existence (Modern Horizons 3 #174)
Thought-Knot Seer (Oath of the Gatewatch #9)
Walker of the Wastes (Oath of the Gatewatch #10)
Warping Wail (Commander Masters #812)
Wastescape Battlemage (Modern Horizons 3 #17)
Zhulodok, Void Gorger (Commander Masters #704)

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