Good teammates are those that can induce even more pressure on the opponent. This set will force switches very often, so a 'mon with Spikes, Toxic Spikes, or Stealth Rock is very helpful to wear down 'mons that might stop something else's sweep. Pokemon with good synergy in this case include Qwilfish, Tentacruel, Roserade, Krookodile, and Cobalion, all of which can lay down hazards while often adding more pressure with things like the threat of setup or strong moves. Tentacruel is fun here because its Acid Spray does the same thing as Metal Sound, and sometimes amplifies its effects. Other good teammates synergize well type-wise with Zapdos, and they include things like Swampert, Cobalion (again lol), Doublade, Empoleon, and Jellicent.