Hiiiiiii, Stunfisk. I’ve put together a string of articles on classic OU metas in order to help those getting into the Stunfisk Circuit Old Gens tournament. I talk a lot on discord about how I love old gens (specifically RBY/GSC/ADV OUs), and so now’s kiiiiinda my time to put my money where my typing fingers are. I’ve probably tried to write these articles a dozen times, but I’ve never been satisfied with them. But! The tournament is going to be soon, so it’s now or never. With that, here we go!
This article will focus on RBY and the major mechanics that have changed that will most likely impact your tournament play. This isn’t an exhaustive list; RBY is a mess on the coding end, and there have still been big revelations within even the last few years of how the mechanics work (Normal immunity to BS Para),  and honestly I know I will miss some very specific interaction of mechanics. So I’m just putting a disclaimer that I’m sticking to the big ones. (If you know of a mechanic not listed, comment it!)
Topics Covered:
1. Abilities/Items
1b. Dark, Steel, and Fairy (and effectiveness changes)
2. The Special Stat
2b. Physical/Special split  (or, the lack thereof)
2c. Other Stat Stuff
3. Critical Hits
3b. Multi-Hit Moves
4. Status
4a. Freeze
4b. Body Slam and Normal Types
4c. Sleep (Rest)
4d. Poison/Toxic
4e. “Cleric Clause”
5. Everything Can Miss Syndrome
6. But wait, there’s more?
1. Abilities/Items
This is probably the easiest to explain and also the most obvious. (That’s why it’s first!)
Simply put: Items and abilities don’t exist in RBY. You have a Pokémon, you have four moves... And that’s it. You cannot get passive recovery from Leftovers, as Lefties doesn’t exist until GSC. There are no Choice items until gens 3/4 (Band in 3, Specs/Scarf in 4), so no Pokémon is locked into a move unless it’s a move that naturally spans multiple turns. And of course, no Trainer items in battle, so... You’re stuck with what you have.
On the topic of abilities, when you import/export an RBY team, you might see abilities listed in the output, but that’s just how the teambuilder is built. They’re not actually in effect, so ignore that. Tauros does not actually have Intimidate, Mew does not have Synchronize, etc. It’s just a visual error, at most.
1b. Dark, Steel, and Fairy types (And effectiveness changes)
Also: Dark, Steel, and Fairy types don’t exist in this generation at all. Dark and Steel don’t exist until GSC, and Fairy doesn’t exist until XY. So, Magneton (not that it’s used in RBY OU) is only an Electric type; it isn’t a Steel type yet. Clefable, likewise, is only a Normal type at this point. Don’t make a dumb mistake where you click a move and then realize, Wait! That didn’t do super effective damage!
Also, there are some effectiveness changes between RBY and other gens:
Ice is neutral to Fire. This means Charizard and Moltres are weak to ice, rather than overall neutral. This is relevant with all the Blizzard and Ice Beam spam that happens.
Poison is super effective on Bug, and Bug is super effective on Poison. Not that there are many Pokémon using those types of moves in the first place, but...
Psychics are immune to Ghost. Alakazam takes no damage from Lick. Yaaaay.
Fixed damage moves don’t check typing. You can Night Shade an Alakazam, and you can Seismic Toss a Gengar.
Now, on to some actual nitty-gritty!
2. The Special Stat (And Stats in General)
In RBY, there are the following five stats: HP, Attack, Defense, Special, and Speed. Special Attack and Special Defense as we know them do not exist. Special in this game refers to both at the same time. It is not until GSC that Special breaks into Special Attack and Special Defense. (And even then, for the purpose of backwards trading, the Special DV is still fused in those games.)
What does this mean for RBY Pokémon?
It means that Pokémon that usually have a high Special Attack or Special Defense in later generations will have a hefty stat that controls both their offense and their defense. Take Chansey as a prime example: In GSC+, Chansey has a Sp. Atk of 35 and a Sp. Def of 105. Basically, it’s not going to hurt you with actual attacks outside of like Seismic Toss because that damage doesn’t scale with stats. But, in RBY, the Special stat is fused, and so Chansey has that Special of 105 from which it can fire off Ice Beams/Blizzards/Thunderbolts that actually have some bite behind them.
Additionally, this fused stat impacts stat drops in a big way. The move Psychic in GSC+ can lower a target’s Special Defense. In RBY, it’ll just drop your Special as a whole. Both your offensive and defensive power will drop. This is how Psychic types can brute force their way through Pokémon that would normally check them: If you drop a target’s Special enough, you can just ram your way through their defenses, and their Special attacks will do less and less to you in return.
2b. The Physical Special Split
All generations before DPP use a different system to determine if a move is physical or special. Rather than each move having its category bound to it, you have a system where the type determines what category the move falls under. A quick way to remember what is what is that all special move types have an Eeveelution—and then Dragon because Dragons are special mythical creatures.
By that, you have Fire (Flareon), Water (Vaporeon), Electric (Jolteon), Psychic (Espeon), Dark (Umbreon)*, Grass (Leafeon), and Ice (Glaceon). Plus Dragon*.
*Dark and Dragon’s special category doesn’t matter yet in RBY. Dark, as stated, literally doesn’t exist, and Dragon’s only move so far is Dragon Rage. But for the sake of fullness and for reference for GSC/ADV, it’s also included here.
If a move is not listed under those typings, it hits off of Attack and Defense. If it is one of those typings, it’s using Special.
2c. Other Stat Stuff
IVs and EVs don’t exist in this gen. Instead, you have DVs and stat experience. The main point of the difference is that DVs range up to 15 instead of 31; in GSC, they determine gender and shininess, but that doesn’t matter yet. Stat experience is a bit more practically different: In RBY, when you defeat a Pokémon, instead of dropping “+1 Sp. Atk EV” or something like that, you gain stat experience equivalent to the defeated mon’s base stats and there’s a complex formula and... Basically, it’s like Hackmons: You can fill every stat to the max. Because of that, all stats are basically set in stone; there’s no customization. You can, technically, drop your DVs, though... I can’t actually think of a reason why you would do that, outside of Counter shenanigans. (And I personally don’t think that’s a good decision, but you do you.)
ALSO. DO NOT CLICK THE GREY SUGGESTED SPREAD TOOLBOX IN THE TEAMBUILDER.
Clicking the suggested spread will not visually do anything, but it’ll mess with I think the stat experience and it’ll basically ruin your stats. There was a mystery for a while where people asked, “Why didn’t my Tauros do this amount of damage?” And it turns out they had clicked that button. Don’t touch it. It’s not needed.
3. Critical Hits
Critical hits are central to RBY play. Crits are not based on a fixed rate; instead, they’re based on the mon’s base Speed stat! (Because of course faster mons have the innate ability to suddenly do double damage! Such an obvious choice!) The faster the Pokémon, the more likely they are to get critical hits.
If you want to know how it works, Bulbapedia [explains it on their page on Critical Hits](https://bulbapedia.bulbagarden.net/wiki/Critical_hit):
Basically, the probability P of getting a critical hit for a normal move is P = Base Speed/512. For a move with a high-crit ratio (Slash being the most common): P = Base Speed/64. (Yes, any moderately fast mon who is 64 Speed or above with Slash has a guaranteed crit off of Slash.)
Focus Energy, by the way, is broken. Not in the “Mega Rayquaza is BROKEN” sense; in the “My brother broke my things and they won’t work!” way. Focus Energy was, it seems, supposed to increase the crit ratio by x4. However, it seems that the way in which Focus Energy was written multiplies the denominator of the formula, which... Had the exact opposite effect as intended. If you use Focus Energy, your critical hit ratio plummets from Speed/512 to Speed/2048.
A word on how crit damage works: In this generation, critical hit damage is about double damage, as opposed to XY+ where the damage is a strict x1.5. It’s not exactly double in RBY because it uses a different formula from GSC-BW2: The formula basically means lower-levelled Pokémon have smaller boosts from crits, but at level 100 it’s within a few hundreths of double. (Don’t worry about it very much.)
Something that you should worry about: Crits ignore ALL multipliers that would affect damage. This sounds good in theory, but it might not be in practice. Because no multipliers get activated, any boosts to your stats will not count (so if you boost above 2, you’re going to do less damage) and any drops on your opponent will not count (so if you’re trying to break them down with multiple Special drops and you crit, you might actually do less). Crits also ignore Burn. Reflect, etc. as they’re multipliers too, but the stat boosts not being counted is probably the wonkiest thing.
3b. Multi-Hit Moves
Multi-hitting moves are not very common in this generation, but an important thing to note: If one hit is a critical hit, every hit will be a critical hit. For example, if Jolteon gets a crit on the first Pin Missile, then every single Pin Missile will land a crit. So, you can get hit with five crit Pin Missile hits in a row if Jolteon is really lucky. Yikes.
4. Status
Status is a critical part of RBY battles. Most battles will open with sides seeking to exchange either Sleep or Paralysis. Knowing how the statuses work in RBY is important to managing your team during a battle, especially in a generation without Heal Bell.
4a. Freeze
Freeze is the scariest RBY status effect. You know how in other generations you can thaw out?
Yeah, you can’t thaw in RBY on your own.
There are three ways to escape freeze in RBY: (1) You use an Ice Heal, which is not going to happen in battle for obvious reasons; (2) Haze goes off and clears your status condition because that is what Haze can do in this gen, but because RBY is all Singles, your opponent has to be nice and do that for you; or (3) you get hit with a fire type attack like Fire Blast, and... There is nothing ranked OU that commonly carries a fire move at all. So you have to depend on your opponent running non-standard moves and you have to have your frozen mon in as that move happens.
Basically if you’re frozen, it’s a practical death.
Which is why sometimes you’ll see people throw Blizzards and Ice Beams into Chanseys because if you roll that 10% chance you’ve just cheesed your way through an annoying, bulky mon with consistent recovery. (I’ve personally had people switch to Chansey on my lead Jynx and I just clicked Blizzard until I got a freeze. It’s a Thing You Can Do.)
4b. Paralysis
Paralysis. The yellow magic. We all know and love it.
Paralysis in RBY is mostly the same as it has ever been. Thunder Wave is commonly run on Zapdos, Starmie, Chansey, and Alakazam, just to name a few. Thunder Wave can paralyse Electric types, so be careful if you’re trying to finish with Zapdos, as it is able to get caught by Thunder Wave.
Body Slam is the other main method of spreading paralysis, and there is an important and rather new side note to talk about here. Body Slam is most commonly carried by Tauros and Snorlax, and as they are some of the best mons in RBY, there is a key mechanic at play: Body Slam cannot paralyse other Normal type Pokémon. No matter how many times a Tauros Body Slams Snorlax, it will not get paralysed off of Body Slam. This is a change that was discovered a couple years ago, and so in the grand history of RBY simulation that mechanic was missing. (Missing mechanics is not restricted to RBY: ADV simulation missed an important part about how Sleep Talk worked in that generation until recently. More on that Eventually TM.) This means that you can switch a Normal type into Body Slam without fearing status. (Of course, with Tauros’s crit rate, you want to fear the potential damage still.)
Stun Spore is basically restricted to Exeggutor’s fourth moveslot. (The other big three being Psychic/Explosion/Sleep Powder, which almost all Eggy will have. People have played around with that last slot and so Stun Spore isn’t 100% guaranteed.)  Fortunately, it can miss, unlike Thunder Wave.
In general, if your lead is not a sleep lead (discussed below), your lead will often carry a paralysing move. Exchanging Thunder Waves or Lovely Kisses or Hypnosises is a common start in RBY matches. Also, on another play style note, many players will intentionally get Chansey paralysed so as to prevent any chance of the freeze cheese happening. Switching Chansey into an Alakazam’s Thunder Wave is a
4c. Sleep (And Rest Mechanics)
Sleep is rough in RBY. You can sleep for up to seven turns in this generation before waking up, and you cannot move on the turn you wake up. (Waking up is the whole turn, in other words. “Tauros woke up!” is all that will happen.)
There are three main ways to spread sleep onto the opponent: Lovely Kiss, Hypnosis, and Sleep Powder.
Lovely Kiss is restricted to Jynx in this generation, and Jynx will almost always lead a team. Among seasoned players, I have never seen a Jynx outside of lead position. It is my personal favourite lead: With 95 Special and Speed, Lovely Kiss, and two wicked STABs in Psychic and Blizzard it can sleep a lead and then get a few nice special hits off.
Hypnosis is basically only on Gengar. It’s also the worst sleep move, as it is only 60% accurate compared to Lovely Kiss’s and Sleep Powder’s 75%s. If a team has a Gengar, it can often lead, but I have seen Gengars in the back.
Sleep Powder is one of the many things that makes Exeggutor good. Exeggutor almost always carries Sleep Powder, and with 125 Special it will often be able to drop the sleep sometime during a match. Often, an Exeggutor will then proceed to Stun Spore the switch-in after a player switches out their sleeping Pokémon in a tactic called Double Powder. This leaves the opponent with a sleeping mon and a paralysed mon, and Exeggutor is free to Psychic or even threaten an Explosion. It’s nasty stuff.
The upside of sleep is that your opponent can only sleep one Pokémon at a time. (This does not count Resting Pokémon.) So if your lead falls asleep, you can’t get anything else put to sleep.
Speaking of Rest: Because of how sleep works, you’re only “asleep” for one turn, but your second turn is you waking up, so you spend the same amount of time inactive as you do today. (“Snorlax used Rest!” -> “Snorlax is fast asleep!” -> “Snorlax woke up!” -> “Snorlax used Body Slam!” is four turns of battle.)
4d. Poison/Toxic
Everything in RBY that learns TMs can learn Toxic, but nothing runs it. You can theorymon that Toxic/Wrap is a potent strat and whatnot, but nothing ever seems to be able to fit it in their moveset, and the damage output never seems to add up to enough. You can try to make it work, but it’s not something that I’ve ever seen have great success, so if you pull it off, kudos to you.
An interesting note about Toxic: The game does not remember if a Pokémon is poisoned or badly poisoned as it switches out. Thus, if you bring in a toxiced Pokémon, you will see the Toxic be converted to normal Poison. It’s just how the game remembers things.
4e. “Cleric Clause”
If you really want to be technical, in RBY and GSC your party Pokémon enter a link battle exactly as they were in the overworld. If they were missing HP, missing PP, had a status, etc. that is not auto-healed away when a link battle begins.
Showdown is not configured to allow this, and it has not, to my knowledge, ever been a Thing that a sim allowed you to do. There is a de facto “Cleric Clause” stating that all Pokémon are assumed to be totally healed in the instant prior to the battle beginning.
A question that has been asked is: What would be better without Cleric Clause? The general consensus is Chansey, Alakazam, and Starmie would be better. You would enter battle with those three burned, and they would then act as status sponges. You couldn’t freeze them, paralyse them, or sleep them, and they can easily Recover or Softboiled off the damage that eventually racks up with burn. The attack drop from Burn even reduces self-hit damage from confusion, so it’s a “perfect” kind of build that improves those Pokémon. (You get into fun stuff like 1HP Flail in GSC, but those times are yet down the road.)
5. Everything Can Miss Syndrome
Fun fact, nothing is really guaranteed to hit in RBY. Moves that are 100% accurate are really 255/256 accurate. There is a 1/256 chance that a move will miss, even if you have no accuracy drops. You can miss Earthquake and Body Slam just because the rng hates you in that second.
Which, really, means you should never forfeit when things look bad. Arceus may take pity on you and give you that 1/256 chance so that you avoid a Body Slam and KO in retaliation. There’s always a less than 1% chance that things much just turn around.
Because of course there is an exception to this: Swift doesn’t check accuracy period, and so it’s the only thing that can’t ever roll that 1/256.
But other than that, everything can miss. (Even the Master Ball can fail in-game if you’re very unlucky.)
6. But wait, there’s more?
Yes, there’s more. I initially wrote this as one huge article that had like a dozen moves and how they’re different in RBY, but.... It got too long. It was a mess. So, I’m separating this out into two articles. This is meant to cover overarching mechanics, and the second article focuses specifically on moves and their individual mechanics. And there are some funky things happening there. Check it out!