12 cards where the number of colors is 4

A-Omnath, Locus of Creation (ZNR)
Atraxa, Praetors' Voice (2XM)
Breya, Etherium Shaper (2XM)
Dune-Brood Nephilim (GPT)
Glint-Eye Nephilim (C16)
Ink-Treader Nephilim (GPT)
Kynaios and Tiro of Meletis (C16)
Omnath, Locus of Creation (ZNR)
Saskia the Unyielding (C16)
Witch-Maw Nephilim (GPT)
Yidris, Maelstrom Wielder (C16)
Yore-Tiller Nephilim (GPT)

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