Writing up Zangoose.
Zangoose
What effect did Zangoose have on the metagame?
Zangoose has always lurked around in NU, but back then it was just your regular Normal-type with high Attack and good Speed: 115 Attack and 90 Speed are by no means bad. However, the existance of other Normal-types such as Swellow, Braviary, Tauros, Kangaskhan, Ursaring and Cincinno were either much faster, much stronger, or in Kanga's case more reliable, so there really wasn't any point to using Zangoose over a more effective Normal-type. That is until it received its DW ability Toxic Boost, which bolstered it as a threat so much that it leaped nearly 80 spots in usage and was even nominated as a suspect in Stage 5, due to the perfect neutral coverage it always had combined with its newfound power. Carving its name down as one of the most powerful Normal-types, if not attackers in NU, Zangoose terrorized almost everything slower than it with its nearly unparallaled strength, and above average speed for its time meant that those range of targets is wide. Never mind that its health is decreasing every turn, it is unlikely your team would be in better condition by the time Zangoose drops dead.
In what main roles was Zangoose used?
Effective but one-dimensional, Zangoose aims for nothing more than to rip its opponents to shreds. However, how one did it was another story altogether. The item choice is obviously and should always be Toxic Orb: using Life Orb or Choice Band would be completely redundant whereas Choice Scarf is done better by Tauros or Kangaskhan who have more useful abilities. Zangoose has 5 moves to choose from: Facade, Close Combat, Night Slash, Swords Dance, and Quick Attack. Unfortunately it cannot fit all of them into the same moveset, so Zangoose often has to choose between KOing walls with Swords Dance, threatening sweepers with Quick Attack, or do both while giving up a coverage move. Zangoose's main prey are slower targets that get KOed easily by its attacks, and capitalize on the fact that few dare to switch in on it.
What caused it to have a significant impact?
Swords Danced Toxic Boost poisoned-Facade. Name me one non-Normal resist that can switch into this without risking a OHKO....I thought so. Even its non-Swords Danced Facade was hard enough to switch into for most Pokemon. Zangoose's claim to fame is that between its boosting move, perfect neutral coverage and even priority, Zangoose has the potential to KO anything in the tier. Rock- or Steel-types get pummeled by Close Combat, Ghosts are shredded by Night Slash, and any revenge killer had better be in good shape lest a Quick Attack pick them off. It is notoriously difficult to avoid losing a pokemon to Zangoose, since the only pokemon that can survive Zangoose's attacks are slower than it (those switching into Zangoose are exposed to 2 hits or worse, Swords Dance), while those faster than Zangoose cannot switch in at all unless they come in on a weaker/resisted attack.
How do/did you deal with this Pokemon in NU?
Zangoose suffers from a design flaw: it needs to wait a turn to activate Toxic Boost. This is pretty much the best window of opportunity for your faster sweeper to switch in on its unboosted attacks and threaten it out or KO it due to its dwindling health and poor defenses, the latter of which could be further dropped by the use of Close Combat. This isn't always that simple however, as Zangoose may Swords Dance on the switch and use the subsequent Toxic Boost to overpower your faster pokemon with Quick Attack, or Zangoose can activate Toxic Orb without having to waste a turn via a teammate's Volt Switch/U-turn/Baton Pass. The former makes Haunter a special case, as it is faster than Zangoose and immune to Quick Attack, making it a great offensive answer to Zangoose, while Intimidate Tauros can cushion the blow. Defending against Zangoose is much harder due to its power, but since it is losing health every turn, predicting around Zangoose's attacks using the team's resistances and defensive synergy, or stalling it with Protect or Substitute, can still overcome the cat ferret, even without actually fighting back. A Zangoose without Swords Dance is going to have much more trouble against the likes of Tangela, Alomomola, Armaldo, Torkoal and Regirock, all of which can survive the attack and either outstall Zangoose so it succumbs to poison or attack it directly to speed up the process. Zangoose's fraility also made Swords Dance tricky to use in the first place, so that offers yet another chance to whittle it down before it gets going. Finally, priority targets Zangoose's frail defenses and bypasses its speed stat, or force it to use Quick Attack to overtake slower priority users. Even if the attack does not KO, any extra damage on Zangoose shortens its lifespan and resultantly sweeping time. Pokemon such as Carracosta, Swellow, Piloswine, Gurdurr and Skuntank are all popular priority users that can pressure Zangoose, though keep in mind a slower Sucker Punch fails against Quick Attack. While circumstantial, if you can make Zangoose lose its Toxic Orb via Trick or Knock Off before it activates or inflict it with any status aside from poison, Zangoose is effectively neutered, although Facade is still boosted from paralysis and burn.