Pokemon versions Red/Blue/Yellow stand out as being some of the glitchiest video games ever made. Some would argue, however, that the glitches give these versions their own, unique charm, further backed up by GameFreak's removal of many of these glitches in all future versions of Pokemon.
This is a list of everything that works differently in RBY.
Instead of being divided in Special Attack & Special Defense like in GSC, RSE, or DPP, there is only one Special stat in RBY, which covers both Special Attack and Special Defense. Every move that raises or drops the Special stat, such as Amnesia or Psychic, will therefore affect the Pokemon's ability to both use special attacks and take special hits.
In RBY the critical hit ratio is based on base Speed rather than having a set ratio. This means that faster Pokemon will critical hit more often than slower ones. This is very important to consider in RBY as most of the faster Pokemon will have a critical hit ratio higher than 20%. It is important to note that the critical hit ratio, being based on BASE Speed, will not change if the Pokemon is paralyzed or suffers a Speed drop, so attempts to reduce critical hits through these methods are futile.
Formula to calculate a Pokemon's critical hit ratio : CH%=BaseSpeed*100/512.
In addition, when moves critical hit, they will ignore any stat change both the attacking and defending Pokemon have, beneficial or otherwise. For example, if the attacker uses Amnesia 3 times to maximize its Special stat and then scores a critical hit, it will actually do less damage than if it didn't critical hit, only doing twice the damage of a normal attack without the boosts. Critical hits will also ignore Reflect and Light Screen.
Razor Leaf, Slash, Crabhammer, and Karate Chop are attacks with a greater chance for a critical hit. Like normal critical hits, they are also based on base Speed, but the formula is slightly different, almost guaranteeing a critical hit on every attack.
Formula to calculate a Pokemon's High Critical Hit ratio: CH%=BaseSpeed*100/64.
There are only two ways to unfreeze: being hit by a Fire-type attack or being in play when your opponent uses the move Haze. The frozen Pokemon will never thaw by itself.
Multi-hit and partial trapping moves always do the same amount of damage each hit; that is, whether or not the attack critical hits and the damage dealt as a result of that calculation, is done once, on the first hit, and carries through for the remainder of hits in succession.
These attacks (Horn Drill, Fissure, Guillotine) are based on Speed but not on base Speed. The attack will always fail if the attacker is slower than its opponent. It may only succeed if the attacker is faster or has the same Speed as the defender and attacks first. The accuracy of a One-Hit KO Attack does not increase depending on your Speed.
Wrap, Fire Spin, Clamp, and Bind prevent your opponent from attacking after they hit during the whole 2-5 turns the attack may last instead of preventing switches. So, if you are faster than your opponent, you can keep using Wrap over and over again and they cannot hit you back. Only the first hit of the 2-5 attack sequence wastes a PP and is subject to miss due to accuracy. The Wrapping Pokemon isn't allowed to use any other attack until the 2-5 turn sequence ends. In addition, a critical hit is only calculated for the first hit; if it does score a critical hit, every remaining sequence hit will do that amount of damage. Using a trapping move can also be used to get a free switch. For example: Cloyster uses Clamp on an incoming Starmie. Cloyster can switch out freely the turn after while Starmie will stay immobilized for that turn, but will still be released from the Clamp. The Pokemon will also remain immobilized if the user of the partial trapping technique is fully paralyzed mid sequence, but the sequence will end.
If a Wrapped Pokemon switches out while in the middle of a Wrap sequence, the sequence resets, and the accuracy must be tested again on the switch-in and another PP is wasted. If at such a time the trapping move has 0 PP, it will still be used against the incoming Pokemon. After that use, the current PP of the trapping move will roll over to 63.
If the target of the partial trapping move just used Hyper Beam, it won't have to recharge if the partial trapping move misses on the recharge turn. Additionally, if the user of the partial trapping move attacks before the user of Hyper Beam during a recharge turn and the partial trapping move misses, the user of Hyper Beam will automatically use Hyper Beam during that turn. If at such a time Hyper Beam has 0 PP, Hyper Beam will still be used, and its PP will roll over 63.
A final interesting note concerning only Wrap and Bind, is that while as they are Normal-type attacks and deal no damage when used against a Ghost-type, they will still immobilize it.
There are a few differences when it comes to a type's effectiveness against another type in RBY.
Of further note, the Steel- and Dark-types, which exist in all other games, are not included in RBY. Therefore, Magnemite and Magneton, who are Steel-types in the future, are here solely Electric-type Pokemon, and attacks like Bite are no longer of the Dark-type (specific instances will be covered later in this guide).
There are three types of stat changing moves: those that boost stats, those that reduce stats, and status ailments which also negatively effect stats. To give an example of each, the first includes attacks that raise a stat by one or two levels such as Sharpen or Agility; the second, attacks that reduce a stat by one or two levels such as Growl or String Shot; and the third, the status ailments or paralysis and burn which lower Speed and Attack respectively. Technically, there is also a fourth category, that of attacks which can also reduce or increase a stat such as BubbleBeam or Rage, but the mechanics do not differ in any way from the first and second types already mentioned so there is no need to separate this class.
Defining the different classes is necessary due to their strange interaction. In RBY, if a Pokemon is afflicted by either paralysis or burn, the third type, it can neutralize the loss by using either a Speed boosting move like Agility, in the case of paralysis, or an Attack boosting move like Swords Dance, in the case of burn. On the flip side, if after having rectified the stat problem in this way a Pokemon is hit with either a Speed reducer like String Shot, in the case of paralysis, or and Attack reducer like Growl, in the case of burn, the stat affected will return to the levels created by the status ailment before boosting again.
When put to sleep, Pokemon never wake up and attack on the same turn. Pokemon take a turn to wake up and are only allowed to attack again the turn after that. This allows a faster Pokemon to put a slower Pokemon back to sleep without fear of being hit while the slow Pokemon wakes up. It should be noted that the application of this mechanic does not mean a Pokemon will sleep an extra turn in RBY when using Rest, however.
When deciding whether a move that targets the opponent hits, or whether or not a move will critically hit, RBY mechanics formulate certainty as a value between 0 and 255, which is capped at 255. For instance, when Persian uses Slash, even though base Speed * 4 = 460 which is well over 255, it's brought back down to 255. The cart then randomly generates a number between 0 and 255 and, and if that number is less than 255, the move hits / critical hits.
Due to this, there is always an extra 1/256 chance that any "100% accuracy" attack will miss, and that any high critical hit rate attack will miss (+~0.4%). The only exception is Swift which does not perform this check and, thus, cannot possibly miss.
When a Pokemon's HP is 255 or 511 below its max HP, recovery moves like Rest, Recover, and Softboiled will fail. For instance, if Chansey is at 192 HP, which is 703 - 511, Softboiled fails.
This attack is able to counter damage taken as the result of a Normal-type or Fighting-type attack (it will fail against other physical type attacks), including reversed damage (from Counter/Bide), Seismic Toss damage, and recoil damage. On multi-hit moves such as Fury Swipes, only the last hit can be Countered. Thus, a Fury Swipes user would not be in too much danger from Counter. The amount of damage Countered is not influenced by type and will hit Ghost-types.
Counter in RBY can be used to counter back damage done on previous turns and not just on the same turn that it is used as long as the opponent's Pokemon doesn't use any move. This includes turns during which an opponent is switched out, is frozen or defrosted, is fully paralyzed, or uses the non-damaging turn of a multi-turn move such as recharging, gathering sunlight, or glowing. For example: an Alakazam uses Seismic Toss against an opposing Chansey as it switches in; if the Alakazam switches with Tauros, and if the opposing Chansey uses Counter, Tauros will take the 200 damage reflected from the last turn.
Interestingly, Counter can critically hit, though it does not do a different amount of damage than it would have ordinarily. Also, this attack can work when the damage is done to the Substitute (even when the user has a Substitute) to Counter back the amount of damage that would have been done to the user. This allows Counter to counter back damage that is up to double the user's HP; think Explosion and Selfdestruct. The exception to this is Countering a OHKO from behind a Substitute, which causes the Counter to fail.
During the underground phase of Dig and the "Flew up high!" phase of Fly, the Pokemon using Dig is immune to Earthquake and the Pokemon using Fly is immune to both Thunder and Gust.
Now the interesting part is if a Pokemon is fully paralyzed or hits itself in confusion while underground/in the air, not only will it stay there until it either switches out or uses Dig/Fly again, but it will also keep the invulnerability until it switches out or uses Dig/Fly again! The Pokemon will be able to use any other attack it may have and remain invulnerable to any attack (except Swift, Bide, and Transform) as if it were still underground/in the air.
Hyper Beam does not require a recharge turn if the opposing Pokemon faints as a result of the attack, the Hyper Beam breaks a Substitute, or the Hyper Beam misses. If playing under Pokemon Stadium rules, however, this glitch is fixed and Hyper Beam works as in the future generations.
Reflect and Light Screen double the user's Defense instead of halving the opponent's Attack. Both moves are permanent until switching out. A critical hit will also ignore them, and Haze cancels them.
While using Rest removes Status effects like paralysis and burn, it does not allow the Resting Pokemon to regain the stat loss suffered from either of them until switched out.
Both moves have no use whatsoever in link play. Unlike in the later versions they do not force switches; they just have no effect. Whirlwind also only has 85% accuracy.
A Substitute will not block status ailments except poison. It also blocks confusion moves such as Confuse Ray and stat reduction moves such as Screech. Substitute will block attacks' secondary effects (ex: Body Slam can't paralyze if it hits a Substitute, unless it breaks) except for secondary confusion. Substitute will not block the effect of partial trapping moves. A Substitute will also be the recipient of self-inflicted confusion damage. Lastly, HP draining attacks used on a Substitute will not drain HP when breaking the Substitute.
Pokemon Stadium fixed this glitch, causing Substitute to defend against status as in future generations.
Secondly, if the attacks Selfdestruct, Hyper Beam, or Explosion are used on a Substitute and the Substitute breaks, the consequences of these attacks do not occur. That is, the Pokemon using Selfdestruct or Explosion will not faint, and the Pokemon using Hyper Beam will not need to recharge.
Using Substitute at exactly 1/4th HP will cause the user to faint.
Very roughly, using both in combination will make Leech Seed absorb more and more damage as Toxic's damage also increases.
In more detail:
Consider a variable N which removes N/16 of the Pokemon's HP, referenced by both Toxic and Leech Seed. With Leech Seed, N normally isn't increased each turn, but with Toxic in effect as well, the counter is increased twice each turn, once after each of these recurrent effects. For instance, 1/16 from Toxic and 2/16 for Leech Seed, 3/16 from Toxic then 4/16 from Leech Seed, etc. By the fifth turn of that effect, it will OHKO the Pokemon. Both are reset to 1/16 and don't increase again the first time you switch out, however, just like Toxic by itself.