Welcome to the formulaic but unpredictable world of RBY. This is the first generation of Pokemon, a simpler time, before items, abilities and EVs and with only 151 Pokemon to worry about. But be aware, being the first generation also means RBY has a few quirks—you might call them kinks that got ironed out over the generations.
RBY is a centralized, unbalanced and very limiting metagame. There is very little room for surprises and your team will most likely be all but identical to your opponents; this is RBY's appeal. Everything in RBY comes down to your in-battle awareness, a little bit of knowledge, and luck—quite a lot of luck, but if you are going to play RBY you just need to accept that. If you can't, you should stop reading right now. At least you will never have to worry about a battle being over before it starts just because your team is weak to a certain combination (unless you built a particularly bad team, but hopefully this guide will help you avoid that). Whether or not that is better or worse than a battle being over by the second turn thanks to a freeze and a critical hit is probably a personal preference.
What a modern generation player can gain from learning RBY, however, is the ability to hustle. In a game where luck is everywhere—where the worlds greatest player can probably only win about two thirds of the time against an average player—every fraction of a percent improvement you can make to your chance of winning becomes gold. Every time you have to switch an unparalyzed Chansey into a Blizzard is the loss of one of the many micro-battles that make up a game of RBY. You need to learn to scrap for every percentage point, you will need them, and you will be a better player for it.
There are many mechanical differences between RBY and the later generations, even between RBY and GSC. There were no items; the single Special stat existed in the place of Special Attack and Special Defense; critical hits are calculated based on base speed—meaning some Pokemon can get critical hits up to about 4 times as often as in GSC—see this guide for further details; Pokemon will never defrost, unless hit by a Fire-type attack or an opponent's haze; a sleeping Pokemon will not attack on the turn it wakes up; and with the exception of Swift, every move has a 1/256 chance of missing every turn—remember, there is ALWAYS a chance you can win in RBY. A full list of RBY's mechanical differences can be found here.
There are also many differences in the mechanics of specific attacks. The RBY Differences article and the individual attack pages cover these in depth; some important examples include Counter, Explosion, and Substitute, but there are two in particular that are vitally important to RBY and to this article.
The first of these is Hyper Beam. Hyper Beam does not require a recharge turn following a turn it KOes a Pokemon. It doesn't take too much imagination to realize how important this can be. Expect Normal-type Pokemon bar Chansey to have this attack in their set somewhere.
The second of these are partial trapping moves. Anyone who has played the RBY carts will remember this from Erika's gym. Instead of preventing switching, they prevent the opponent attacking for their duration. They can be extremely powerful, especially when paired with Agility; to the point where they have become the source of a lot of debate among RBY players over whether they should be banned or not.
In the good old days, when RBY was the only Pokemon playable online, and even for a long time after that, the insanity of some of RBY's glitches appeared banal when put next to the insanity of the online simulators we used. The Azure Heights's simulator Porygon's Big Show can still be found online ( http://porygon.math.miami.edu:7137/ ). It's something of a historical relic—a monument to how far Pokemon on the internet has come.
It was in that climate that the standards of RBY developed, and over time what I am now calling the seven staples proved themselves the stars of RBY. You can bet you will still see at least three of these Pokemon on any decent RBY team, and it's almost as likely you will see six of them as it is you will see something else. If you understand their roles, you are half of the way to understanding RBY.
Tauros is the undisputed king of RBY—at least since Mewtwo and Mew got banned. As a Normal-type, it has an amazing STAB Hyper Beam, but the real reason for Tauros's place at the top is Body Slam. Tauros gets a critical hit over 20% of the time, and although very little can take a critical hit Body Slam and a Hyper Beam, the real threat is the paralysis chance. Paralysis is precious in RBY; people will do everything they can to stop you from spreading it any further than their Chansey or maybe their Exeggutor. Neither is a wise switch into Tauros.
Chansey got an evolution in GSC, but the irony is that Blissey has never been half as good as Chansey was in RBY. The 308 Special stat counting for both offense and defense helps, but it's really the power of status that makes Chansey such a menace in RBY. If you want to get rid of status in RBY, there is only one way—Rest. Rest means Tauros can switch in for free. You don't want Tauros to switch in for free. Chansey absorbs status—paralysis does little to reduce its effectiveness as a wall against special attackers—and dishes it back out in equal measure.
Snorlax has the same thing going for it as Tauros: it can Body Slam. It gets a critical hit only a little over 5% of the time but it has a hell of a lot of bulk, enough to allow it to switch into a critical hit Body Slam from Tauros and still survive the Hyper Beam, a rare trait. It also has STAB Selfdestruct which, coupled with its bulk, makes it an effective check to pretty much anything.
Sleep is almost indispensable in RBY, and Exeggutor is the best at it. It also learns Stun Spore and Explosion, which are great moves by themselves, but together they give you a chance to scare away a paralyzed Chansey and hopefully inflict more status on your opponents team.
Starmie's critical hit rate is even higher than Tauros's, and it has unresisted coverage, the ability to inflict status, and excellent bulk for a Pokemon with a one turn recovery move. It survives Exeggutor's Explosion at full health, so it is an option for dealing with that. Offensively, however, its usefulness is mostly limited to luring out Chansey, since it has almost no chance whatsoever of killing one.
Alakazam is a special attacker that can beat Chansey, either by lowering its special with Psychic, or just by PP stalling it. It's fast and does a hell of a lot of damage if you don't resist Psychic. It lures Chansey like Starmie does, but the extra damage means you will usually have an easier response. Chansey will have to use Softboiled sooner, allowing you to switch in a physical attacker, and Special drops can force Chansey to switch out, giving you a chance to hit something else with status.
These guys count as one Pokemon, with the choice of Explosion or extra bulk and power. They can Body Slam like Snorlax or Tauros, with less power, but with an extremely strong STAB Earthquake to back it up. Their immunity to Thunder Wave makes switching them in against special attacking Pokemon a bit easier, and they can come in nicely on Hyperbeams, taking not much damage and forcing a recharge, or on Explosions. Their main use, however, is the fact that they beat Zapdos. Zapdos rivals Tauros as RBY's greatest threat, except to teams carrying Rhydon or Golem.
These Pokemon aren't quite as omnipresent, but they can cause a lot of grief to teams built solely around the seven staples. There are other usable Pokemon, but most are just variations on previous themes, or they are really pushing the boundaries of the term "useful."
Zapdos is almost the only mixed attacker in RBY, and it's certainly by far the best. Its STAB Drill Peck keeps Exeggutor and Chansey at bay and for anything else it has an extraordinarily strong Thunderbolt as well as the threat of Thunder Wave. Unfortunately for Zapdos, as stated earlier, if your opponent has a Ground-type, it will struggle to have any impact whatsoever.
Lapras is bulky enough to switch into Tauros, and it hits hard with Blizzard. It has some hope against Chansey with Confuse Ray and Body Slam. It will make switching something else in much easier at the very least.
Jynx is a fast sleep lead, though it is slower than Gengar. It hits hard enough with Blizzard that it can force your opponent into countering it with Chansey (if they don't have a Starmie, for instance) and if so, it has about a one in three shot at freezing it before dying to Thunderbolt.
Another special attacker than can beat Chansey, Slowbro can Thunder Wave and do a hell of a lot of damage with a bit of luck (In RBY, we call it luck when your opponent DOES NOT get a critical hit).
Gengar is here because it's the fastest sleeper. It can explode, and is immune to Body Slam, but really, it's all about that first sleep.
The main difference between the glory days of RBY and now, at least in terms of simulators, is that partial trapping moves are now implemented—if not perfectly correctly, at least adequately. This was the purpose of the earlier historical diversion, because the standard RBY metagame originally developed without Wrap.
Most trappers have little impact on the staples and their roles; Cloyster and Victreebel reach cat status. Cloyster's defense, with Explosion and the power of Blizzard and Clamp, and Victreebel's ability to spread status and 99.6% chance of Razor Leaf landing a critical hit make them significant threats to any team.
Dragonite is a whole other kettle of fish. It can almost cause people to wonder whether or not Tauros really is the best fit for this particular team. After an Agility, it can beat a full health Starmie slightly over half of the time without taking a single hit. The question is, does the fact that that single hit will almost OHKO Dragonite make up for this extraordinary percentage? It certainly makes Gengar a lot more appealing, and it is likely responsible for a big increase in the usage of Lapras in recent years.
Now that you understand the individual pieces of the RBY puzzle, we must turn our attention to the bigger picture. In RBY, the path to victory is achieved through pursuing the three great status effects—paralysis, freeze and sleep.
The classic formula for winning in RBY is pretty simple. You want to paralyze your opponent's whole team, then clean it up with Rhydon and Tauros. This is a solid plan, made even solider with options such as Cloyster and Dragonite, but in reality it will almost never happen unless your opponent is bad. The main roadblock to its execution is Chansey.
Once Chansey is paralyzed, it will do everything it can to prevent you paralyzing everything else. Exeggutor or Alakazam may paralyze a second Pokemon, but once Chansey and a second Pokemon are paralyzed, your special attacking Pokemon will find it hard to spread paralysis any further than that, at least without the help of something that hits physically. You need to punish your opponent for a conservative approach to status. If they switch to Chansey every single time you could use Thunder Wave, then you need to switch in a physical attacker every single time as well—unfortunately, they will probably catch on pretty quickly, but in theory this is the idea. Remember, even fractions of a percent count. Don't let your Snorlax take an Ice Beam as it comes into Chansey if you could just as easily switch the turn Chansey comes out.
Of course, your opponent should be aware of this as well. If, when you have a paralyzed Chansey, you never ever allow anything else to be paralyzed, you are either playing poorly, or you are playing against poor players. This is where awareness is important. Will it matter if your Pokemon gets paralyzed? If it does matter, is it worth taking the risk and staying in anyway? These are not particularly easy questions to answer, but ultimately this is the knowledge that separates the good from the great.
In summary, there are three main ways to spread paralysis beyond Chansey. Some Pokemon with paralyzing attacks such as Alakazam, Exeggutor, and Slowbro can force Chansey out. This will most likely only spread the paralysis to one extra Pokemon, and maybe not even that if they just relieve Chansey with a sleeping Pokemon or predict well. You can make your opponent too scared to bring Chansey in with aggressive switches to physical Pokemon. However, in all likelihood, you will find over half of your paralysis victims come from using Body Slam.
Freeze is a death sentence in RBY. A frozen Pokemon is limited to sacrificing for a safe switch in and taking Explosions. The only reason RBY Pokemon ever defrost is that defrosting is so rare, sometimes people forget it's actually possible and carelessly use Fire-type attacks on frozen Pokemon. Once your one sleep is used, there is only one reason for not paralyzing any Pokemon when given the chance: because you want to freeze something. Generally, there are only two candidates for taking that option—Alakazam, and in that case only in certain endgame situations where you want to kill it with a Chansey, and Chansey itself.
Freezing Chansey turns your Starmie and Alakazam from tame lures into extremely dangerous sweepers, and it allows you to status basically anything you want. Most freezes in RBY result in wins, and (with the possible exceptions of first turn Exeggutor freezes, or miracle lategame Tauros freezes) Chansey freezes are the best freezes.
Jynx was mentioned for attempting to freeze Chansey earlier, but usually if you are trying for a freeze, Chansey will be the one using Ice Beam with its fingers crossed (mostly just because Chansey is used in 90% of teams and Jynx isn't). Your options for dealing with a Chansey trying to freeze you are to just paralyze it and deal with it as mentioned in the previous section or to try and freeze it back.
Trying to freeze it back is obviously not going to work every single time. This is where hustle comes in. As mentioned before, any Ice-type attack hitting your Chansey is always a loss. Conversely, in a freeze war, Chansey being hit with a Thunderbolt is a win. The quicker you can fire off Ice Beams at freezeworthy targets, the less likely it is you will be the one to get frozen.
There is a grey area for a Chansey, where it is weak enough to be KOed by a Tauros Hyper Beam (69% for a KO on average)—or even a greater off-whitish area where it is weak enough to be KOed by a Tauros critical hit Body Slam (82% max)—but it still has higher than 50% health. If you are in a freeze war and are using Softboiled at greater than 50% health, then you are not using Ice Beam as often as you can, but if you are under 82% and Tauros comes in, things could go horribly wrong. Also, remember that Chansey's most likely responses to Tauros are to switch, use Thunder Wave, or Counter; on any of these moves, a switch back to Chansey is at least not terrible.
Sleep is pretty strong in every generation of Pokemon but, like all three jewels of RBY, it is at its best in RBY. Its duration is longer, and slow Pokemon can be kept immobile indefinitely thanks to the fact that a Pokemon doesn't attack on the turn it wakes. Sleep clause, as always, exists in RBY, but unlike other generations, you will almost always want to make use of it. You can expect your opponent to successfully wake a Pokemon from a sleep in less than half of your battles if you play aggressively and usually, the turns spent trying to get a Pokemon to wake come with a significant cost.
The consequence of the strength of both sleep and paralysis is that sleep is generally used as early as possible in a battle—usually the first turn of the battle by at least one of the players. Being the first to sleep one of your opponent's Pokemon is a significant advantage. When you have slept something and your opponent has not, you have a lot more options available to you. You can paralyze Pokemon more freely and there is much less cost in sacrificing your sleeper—in the case of a Pokemon that learns Explosion, that can be a huge advantage. The only question is, how much are you willing to give up to get that advantage?
If you wish to lead with a sleeper your options are Gengar, which is the fastest, but otherwise least useful; Jynx, with good Speed and middling usefulness; a bunch of other BLs and UUs of varying usefulness and speed; and Exeggutor, the slowest but otherwise the best. The only sleeper slower than Exeggutor that should ever be used in a serious battle is Chansey, and it isn't a common lead.
Your other option for a lead choice is to try to prevent these Pokemon from sleeping you. You may not be able to pick a Pokemon that beats every possible sleep lead—Starmie with Psychic, Blizzard, and Surf is as probably as close as you can get. However, it's not great against Jynx, and it is a poor Starmie set generally. Anything with Blizzard gives you a 9% chance of stopping an Exeggutor on turn one. Alakazam often scares off Gengar, possibly allowing you to bring in your own sleeper to get in ahead of your opponent.
If you are leading with a sleeper, you should strongly consider having a backup. This will allow you to stay in safely if slower or tied for Speed. If you are leading with Gengar, it can help you make up for Hypnosis's shaky accuracy. Or you could just risk it anyway—this is RBY after all.
Lead selection is dominated by sleep, but while it is useful to have the first sleep, it isn't vital. Likewise, if you want to paralyze something before using your sleep move, this isn't an insurmountable obstacle. Sleepers make great lures because the Pokemon they lure are generally paralyzed, which is exactly the sort of opponent that Pokemon such as Snorlax or Rhydon like to switch in against. If in the end you don't sleep anything, that may end up not costing you much. It's very good, but it's not vital.