Obsidian Charmaw destroys a nonbasic land on entry, which cripples their Urza Tron lands or Eldrazi Temple/Ugin's Labyrinth setup, and blocks their large colorless threats like Devourer of Destiny. Wear // Tear's Wear half can destroy Karn, the Great Creator is a planeswalker and not an artifact so it won't hit Karn, but it answers Expedition Map or other artifacts they rely on for Tron assembly. Stubborn Denial and Spell Pierce are weak since their key plays are big creature spells and artifacts/planeswalkers that either dodge these counters or are played with excess mana. Keep your low curve and Leyline Binding to answer Ugin, Eye of the Storms and their Eldrazi threats before they can assemble Tron.