Pikachu is very rare, being found only in Viridian Forest with a 5% encounter chance and the Power Plant with a 25% encounter chance. Raichu is not available in the wild.
ThunderStones may be bought in Celadon City. A free ThunderStone is also available in the Power Plant.
Pikachu, Pikachu... how we wish we could say better things about you. Alas, most nuzlockers probably won't see one with their 5% encounter rate, and getting you after that requires a special trip to the Power Plant, where you still only have a 25% chance of appearing. By that point, they've probably found other solutions to the problems of powerful Water-types and Flyers (including the infamous Gyarados).
However, if you do get one, they can prove very valuable. The lousy bulk may place them at risk, but they’re built to outspeed and OHKO opponents weak to their STABs. Surprisingly enough, Pikachu's Attack is as high as its Sp. Atk, giving the option of coverage. And if caught at Viridian Forest, they provide a very handy early Electric-type, giving a player something to abuse against the countless bird derps early on, as well as an easy answer to Misty.
Rival (Route 22, optional): Bulbasaur resists and Charmander has good offenses, but Pikachu can plow through Pidgey and Squirtle with ease.
Gym #1 - Brock (Pewter City, Rock-type): Not unless you want a dead Pikachu. The lack of a good offense made it possible in Generation 1 (with much Tail Whipping and Quick Attacking), but Rock Tomb gives Onix strong physical STAB, spelling doom for Pikachu’s mediocre offenses.
Rival (Cerulean City): Pikachu will dine on roast pigeon tonight. As for the others, Rattata risks OHKOing with Hyper Fang, Charmander will probably win the high-offense low-defense game, and Bulbasaur resists Pikachu’s STAB. Squirtle, however, dies quickly, and Abra falls to stiff breezes as always.
Gym #2 - Misty (Cerulean City, Water-type): Assuming Pikachu is highly-leveled enough to take Water Pulses, it has the advantage. Pikachu’s lack of bulk makes the fight against Starmie dangerous, however. Beware of confusion - Pikachu cannot afford to lose momentum in this battle, especially if it doesn’t outspeed the Starmie.
Rival (S.S. Anne): Similar to Cerulean City, save that now Kadabra poses a threat. While it may be possible to Quick Attack or Slam your way through its pitiful physical bulk, it’s safer to keep to those Pokémon with Electric weaknesses. Paralyzing Kadabra or the starter with Thunder Wave and switching may be an option, but a good offense with other Pokémon is probably better. Also, Kadabra has Synchronize, so paralyzing it will paralyze you as well.
Gym #3 - Lt. Surge (Vermillion City, Electric-type): TM28, a whole bunch of Super Potions, and a great deal of patience makes this possible, but why not grab Diglett instead? A brief note of caution after the battle - though the 60 base power Shock Wave is a nice upgrade over Pikachu’s current ThunderShock standby, Pikachu will learn the all-powerful Thunderbolt naturally at level 26. You’d be much better off waiting and saving the TM for another Pokémon.
Rival (Pokémon Tower): If Pikachu is level 26 or above, you can bash Gyarados in the teeth with a OHKO. If not, it is advised to avoid using it for this battle, lest Gyarados answer the opening ThunderShock by KOing your glass-cannon mouse. Otherwise, it's business as usual. Growlithe is reasonably strong, so only fight it if you have Potions, and Exeggcute resists Electric. Pidgeotto and Wartortle are still Electric fodder, though watch out for counterattacks. Don't get Pikachu killed now! Once it's level 26, Celadon is just around the corner...
Giovanni (Rocket Hideout, Ground-type): Two Ground-types and a beefy physical attacker? How about not.
Gym #4 - Erika (Celadon City, Grass-type): Resistance to Electric makes this a very poor idea. You can tackle her with a Raichu that has a good Normal move, and Secret Power is decent, but you will still be at a disadvantage.
Gym #5 - Koga (Fuchsia City, Poison-type): Beware the Koffings - Self-Destruct will almost certainly kill Raichu. Aside from that, it may be possible to wreak havoc with Thunderbolt, but a physical Gym is not the best choice for your glass-cannon mouse. Muk especially will take many hits to go down, as it was specifically designed to be a special tank. It can also retaliate very hard with Sludge.
Fighting Dojo (Saffron City, Fighting-type): Probably not a good idea. While Raichu can take advantage of the low Special Defense of many Fighting-types, its poor Defense will make it very sorry if the physically powerful enemies live to counterattack. Especially those stupid Machokes that are never OHKOed and always use Revenge. Many a Pokémon have died to that sick combination.
Rival (Silph Co.): Avoid everything but the Water-types and Flying-types (and possibly Growlithe). Dispatching Gyarados (or Blastoise, if you chose Bulbasaur) makes Raichu a very useful team member for this battle.
Giovanni (Silph Co., Ground-type): Possible to bring it in against Nidorino, but the rest is a wash.
Gym #6 - Sabrina (Saffron City, Psychic-type): Hit hard with Strength or Return. 60 HP/80 Sp. Def is middling, but it could do in a pinch. Paralyzing the Abra-line Pokémon is valuable enough that Raichu might be worth bringing for status purposes alone, although keep in mind that they’ll paralyze you back with Synchronize.
Gym #7 - Blaine (Cinnabar Island, Fire-type): Neutral matchup. Thunderbolt is always mighty, but beware of Stomps and Take Downs from Blaine's Pokémon - 60 HP/55 Defense is asking for a disaster.
Gym #8 - Giovanni (Viridian City, Ground-type): TL;DR: GROUND-TYPE.
Rival (Route 22, pre-Elite Four): Blastoise, Gyarados, and Pidgeot fear Raichu's might. Alakazam is possible with strong physical attacks, but beware Psychic. Avoid Venusaur, Exeggcute, and Rhyhorn. Charizard is possible but risky - if it outspeeds, say hello to Slash and a likely goodbye to Raichu. Growlithe is unevolved, so it's probably manageable.
Elite Four Lorelei (Indigo Plateau, Ice-type): Live fast, die young, and leave an electrocuted corpse. Beware any physical moves from Lorelei - Lapras in particular has a deadly Body Slam. Aside from that, Raichu can take on everything besides Jynx with STAB super-effective Thunderbolt. Viva la Lightning!
Elite Four Bruno (Indigo Plateau, Fighting-type): Strong physical attacks and Ground-types? No thanks. The Hitmons both have a surprising amount of Special Defense, while Machamp is very bulky. Definitely not a good idea to use Raichu here.
Elite Four Agatha (Indigo Plateau, Poison-type): Take out the Golbat. The Ghosts are dangerous and Arbok has good Attack, however, so preferably use a more bulky Pokémon. Beware of status hax - you may want to apply your own parahax out of revenge.
Elite Four Lance (Indigo Plateau, Dragon-type): Demolishing Gyarados in one hit, Raichu nonetheless fears the Dragons' Electric resistance and Hyper Beams. Aerodactyl has 130 base Speed to Raichu's 100, so it's a bad idea to try for a OHKO there (unless you have a Choice Scarf oh wait that doesn’t exist yet).
Champion Rival (Indigo Plateau): Pidgeot, Blastoise, and Gyarados all fear the mouse. Charizard opening with Slash makes the poor creature a goner, but if you’re at a decent level, you should be able to outspeed and OHKO with Thunderbolt. Arcanine has strong physical attacks by now as well as STAB Flamethrower, and everything said about other Pokémon still applies. Yes, Alakazam is still an option, but hopefully you'll have other answers to it by now. Taking out Gyarados is still valuable!
Pikachu should start off with the moves ThunderShock and Growl. ThunderShock is worth keeping for a while, as it’s the only STAB move you’ll have access to for quite a while. Growl can be useful on some occasions, as Pikachu’s physical bulk is notoriously poor. Tail Whip comes at level 6, and is pretty much useless when you get it, since Pikachu only knows specially-based moves at that level. At level 8, you’ll get Thunder Wave, an extremely useful move that allows Pikachu to serve as a status-spreader. Keep in mind, though, that some lines, such as the Machop and Rattata lines, can sometimes have Guts. Quick Attack at level 11 is an okay move, but it won’t even be doing much to the Grass or Electric-types that resist ThunderShock, so it’s a little situational, especially since Pikachu and Raichu have high base speed stats to begin with. The extremely annoying Double Team can be gotten at level 15. You can use it if you want, but relying on hax in a nuzlocke is a good way to get your Pokémon killed. Slam at level 20 should be used as infrequently as possible, as though it has a nice base power of 80, it has absolutely horrendous accuracy, at 75%. Finally, at level 26, you get the amazing Thunderbolt. This is also around the time you should be getting a ThunderStone with which you can evolve Pikachu, so it comes at the perfect time. If you evolve Pikachu, it learns no new moves via level-up as a Raichu; however, if you for some reason keep it as an unevolved Pikachu, you get access to the pretty worthless Agility at level 33 (generally outclassed by Thunder Wave, as paralyzed Pokémon have their speed cut to 25%), the strong but unreliably inaccurate Thunder at level 41, and Light Screen at level 50, which Pikachu and Raichu are altogether too frail to set up, and can be taught with a rebuyable TM either way.
Raichu has a number of nice TM options. Focus Punch and Substitute, as always, combine quite well, Hyper Beam can add some extra power, and you could put Light Screen on your electric mouse if you don’t want to keep your Pikachu unevolved until level 50. A combination of the TMs Rain Dance and Thunder is possible, but you’re probably better off just using Thunderbolt, as the Pikachu line is incredibly frail and might not survive after setting up Rain Dance. Iron Tail can be used for coverage against troublesome Rock-types, but it’s generally outclassed by Brick Break, which is not only much cheaper, but much more accurate and more useful coverage-wise as well. You can try using Dig to take out other Electric-types, but keep in mind that a super-effective Dig does less than a neutral Thunderbolt (unless your IVs and EVs are really screwed up). Secret Power and Strength are also decent, 100% accurate options, while Mega Punch, which can be gotten via Move Tutor, is good for the early stages of the game but should be replaced by Strength later on. Too bad Pikachu that aren’t event-exclusive can’t learn Surf, as that would be amazing for coverage.
Minimum stats are calculated with 0 EVs, IVs of 0, and a hindering nature, if applicable.
Maximum stats are calculated with 252 EVs, IVs of 31, and a helpful nature, if applicable.
Pikachu Line Ratings
What Nature do I want? Raichu exists for Thunderbolt, so Special Attack heightening natures are best. It can afford Speed-lowering natures. Depending on how you use Raichu, you may want it to be able to power Brick Breaks and Strengths, so think twice about Attack-lowering natures. You probably don't want to lower its already awful defenses, though if you plan to use it solely as a OHKO machine, it's affordable. Quiet is probably the best, and Modest is good if you’re not planning to go mixed.
At what point in the game should I be evolved? By the time you hit level 26 and get natural Thunderbolt (saving you the TM for something else/a backup), immediately use a Celadon-bought stone. You'll probably be that level by the team you complete Pokémon Tower.
How good is the Pikachu line in a Nuzlocke? Assuming you can get it, it's pretty good. Beware its awful bulk, however. It proves very valuable in sniping Water-types and Flyers. Charmander users will probably get the most mileage out of it in the long run, but killing Gyarados quickly is always useful. Its usefulness probably peaks twice: in the early-game against Misty, and then against the Elite Four. Pikachu’s awful bulk will continue to give you heart attacks, but if you’re able to get it to level 26, it will return your investment with OHKO after OHKO. It’s always nice to have an Electric-type around, and Pikachu/Raichu are no exceptions.
Resistances: Electric, Flying, Steel
Neutralities: Bug, Dark, Dragon, Fighting, Fire, Ghost, Ice, Normal, Poison, Psychic, Rock, Water