Blood Moon is backbreaking against Eldrazi Tron since their entire manabase (Eldrazi Temple, Ugin's Labyrinth, Urza's Mine/Power Plant/Tower) produces colorless mana, turning it into useless Mountains and stranding Karn, Ugin, and their Eldrazi. Mystical Dispute is a cheap counter for Karn, the Great Creator or Ugin, Eye of the Storms, and costs just {U} against their colorless-heavy deck. Metallic Rebuke is worse here since they run few cheap artifacts to discount it against, and Quantum Riddler gets stranded behind Chalice of the Void or eaten by Kozilek's Command, so both come out. Land Blood Moon early and pressure with Cori-Steel Cutter before they assemble Karn or Ugin lock pieces.