Eldrazi Tron is a grindy ramp deck aiming at Ugin, Eye of the Storms and Emrakul, the Promised End, so Thoughtseize is key to strip a copy of Karn, the Great Creator or a big Eldrazi threat before they can deploy it, and it also lets us play around their sparse interaction. Pick Your Poison's +1/+1 counter and Snake token modes give us a way to build a small threat or chip in extra damage, while its sweep mode is largely irrelevant since their real threats are too big, so it's included mainly as flexible value/pressure. Otherworldly Gaze's surveil doesn't meaningfully progress our game plan against a deck with virtually no pressure to defend against, so it's trimmed, and Golgari Thug is a weak body that doesn't threaten their big creatures or planeswalkers.