Belcher is a fast combo deck built around Goblin Charbelcher and mana acceleration like Lotus Bloom, so Pithing Needle can name Goblin Charbelcher itself to shut off their primary kill condition entirely. Force of Despair is a backup answer if they combo off with creature-based threats that entered that turn, though it's mainly a hedge since their main plan is noncreature damage. Thoughtseize comes out since it doesn't stop Goblin Charbelcher once it resolves and they have plenty of counterspell backup like Disrupting Shoal and Force of Negation to protect their hand; Shadowspear is irrelevant against a deck with almost no combat plan.