Zubat

The nefarious anti-NU PlotBat can be found on almost any NU NFE team, and for good reason. With enough Speed to outpace everything except Cyndaquil, Pidgey and Combee, it can slam nearly the entire NU team with a super-effective hit before being attacked because of its unresisted movepool. Its x4 resistance to Bug, Fighting and Grass attacks, as well as immunity to Toxic and Ground attacks, means Zubat has plenty of opportunities to switch into an attack and set up a Nasty Plot. Giga Drain is a 2HKO on all Water-types in the NU tier, including a max Sp Def Squirtle, and also allows Zubat to recover from Stealth Rock damage and Nasty Plot-turn damage. Air Slash covers almost anything that Sludge Bomb can't, hitting Bulbasaur, Oddish and Bellsprout for a 2HKO. Sludge Bomb is Zubat's main attacking move, slamming everything in the NU NFE tier for a 2HKO bar Togepi, Nidoran-M, Nidoran-F, some forms of Whismur, and Bulbasaur, the latter whom is covered by Air Slash.

Zubat has little need for defenses, and can recover as it is if absolutely necessary with Giga Drain (if the foe doesn't resist it), so Speed and Sp Atk are used in maximizing Zubat's sweeping potential. Modest on Zubat in theory could be used on this set, but Zubat misses out on outpacing Hoppip, some forms of Pichu, and Starly, all of whom can threaten an end to Zubat's sweep. Other Zubats can also threaten this set with their own attacks, making maximum Speed the best overall option.

The classic LeadBat stretches down all the way to the NU NFE tier, denying foes the chance to set up Stealth Rock, and shutting down at least one foe through Hypnosis (assuming it hits). Hidden Power Ice gives Zubat a guaranteed OHKO on lead Gible and Hoppip who aren't holding a Yache Berry, and hits Bellsprout and Bulbasaur for considerable damage. Sludge Bomb covers nearly anything that Hidden Power Ice cannot, and is Zubat's best answer against lead Feebas, Pichu, Igglybuff and Whismur. It also OHKOs the standard lead Turtwig.

If you opt for Wide Lens in fear of Hypnosis' poor accuracy, a switch to 152 Def / 104 Sp Atk / 252 Spd for EVs is recommended. This will still allow you to OHKO the standard Turtwig, and gives Zubat more of a chance to survive a physical attack in the event that Hypnosis still misses. A Life Orb, however, is advisable because it gives Zubat a guaranteed OHKO on a lead Gible, something that it cannot do with a Wide Lens. With a Wide Lens, however, Zubat has an increased chance of putting both Gible and Hoppip to sleep, allowing Zubat to come out on top against either of them should the opponent decide to keep their lead Pokemon in.

The classic LeadBat stretches down all the way to the NU NFE tier, denying foes the chance to set up Stealth Rock, and shutting down at least one foe through Hypnosis (assuming it hits). This allows Zubat to set up its weather of choice while the foe switches, or helplessly stays in. Sludge Bomb is Zubat's best choice in taking down lead Turtwig, and can be used against Grass-types later in the game to inflict considerable damage.

Speed is maximized to give Zubat the upper hand against lead Hoppip and Pichu, who both threaten Zubat through Electric attacks or Sleep Powder, respectively. The Special Attack EVs are needed to ensure the OHKO on a lead Turtwig, and to ensure a 2HKO on Hoppip. The remaining EVs are delegated to Defense to aid in taking Dragon Rush and Brave Bird damage from lead Gible and Pidgey, as well as priority moves later in the game from Squirtle and Ralts.