Dual-type damage misinformation

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Dual-type damage misinformation is a glitch that causes incorrect type effectiveness messages to be displayed against dual-type Pokémon in Generation I games.

Overview

In Generation I, Pokémon with two types that have a weakness and resistance to the same type receive neutral damage from that type, but the incorrect message is displayed.

For example, Grass-type moves do neutral damage to Gyarados, but if Gyarados is hit by a Grass-type move, the game erroneously states that the attack is "not very effective...".

The game prioritizes on which message to display for each 'special' scenario (where normal damage is not dealt) based on each scenario's internal ordering. The higher the ordering determines what message the game will display. Grass against Water as 200% damage for instance is the 4th entry, whilst Grass against Flying as 50% damage is the 27th. Consequently, in this example, the game chooses the message for scenario #27, returning the wrong message "It's not very effective...".

This glitch does not occur in Pokémon Stadium.

By Wooggle
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If an attack is super effective or not very effective against one type and does no damage against another type (for example, Dig against Charizard), the game will erroneously state that the attack missed.

Order of priority of messages

This list is presented in the reverse order to which they are stored in the game data. Messages higher on the list take priority over those lower on the list.

Attacking type Effectiveness Defending type
Dragon Dragon
Ice Dragon
Grass ½× Dragon
Electric ½× Dragon
Water ½× Dragon
Fire ½× Dragon
Ghost Psychic
Ghost Normal
Rock Ice
Rock Bug
Rock Flying
Rock ½× Ground
Rock ½× Fighting
Rock Fire
Bug Poison
Bug ½× Ghost
Bug Psychic
Bug ½× Flying
Bug ½× Fighting
Bug Grass
Bug ½× Fire
Psychic Poison
Psychic Fighting
Flying ½× Rock
Flying Grass
Flying Bug
Flying Fighting
Flying ½× Electric
Ground Poison
Ground Rock
Ground ½× Bug
Ground ½× Grass
Ground Electric
Ground Fire
Poison ½× Ghost
Poison ½× Rock
Poison Bug
Poison ½× Ground
Poison ½× Poison
Poison Grass
Fighting Ghost
Fighting Ice
Fighting Rock
Fighting ½× Bug
Fighting ½× Psychic
Fighting ½× Flying
Fighting ½× Poison
Fighting Normal
Ice Flying
Ice Ground
Ice Grass
Ice ½× Water
Grass ½× Flying
Grass Rock
Grass ½× Poison
Grass ½× Bug
Grass Ground
Electric Flying
Electric Ground
Water Ground
Fire ½× Rock
Fire Bug
Ghost Ghost
Normal Ghost
Normal ½× Rock
Electric ½× Grass
Water ½× Grass
Grass ½× Fire
Fire ½× Water
Psychic ½× Psychic
Grass ½× Grass
Ice ½× Ice
Electric ½× Electric
Fire ½× Fire
Water ½× Water
Ground Flying
Water Rock
Electric Water
Grass Water
Fire Ice
Fire Grass
Water Fire

The text for Dragon being super effective against Dragon is unused as the only Dragon type move in Generation I was Dragon Rage, a move that does a fixed 40 damage to the target that is unaffected by type effectiveness.


Multiple
generations
Transform glitchesGlitch TrainersCloning glitchesError messagesArbitrary code execution
Generation I GlitchesBattle glitchesOverworld glitches
--0 ERRORBroken hidden itemsCable Club escape glitchDual-type damage misinformation
Experience underflow glitchFight Safari Zone Pokémon trickGlitch CityItem duplication glitchItem underflow
Mew glitchOld man glitchPewter Gym skip glitchPokémon merge glitchRhydon glitchRival twins glitch
Select glitches (dokokashira door glitch, second type glitch) • Super Glitch
Time Capsule exploitWalking through wallsZZAZZ glitch
Generation II GlitchesBattle glitches
Bug-Catching Contest glitchCelebi Egg glitchCoin Case glitchesExperience underflow glitch
Glitch dimensionGlitch EggTeru-samaTime Capsule exploitTrainer House glitchesGS Ball mail glitch
Generation III GlitchesBattle glitches
Berry glitchDive glitchPomeg glitchGlitzer Popping
Generation IV GlitchesBattle glitchesOverworld glitches
Acid rainGTS glitchesPomeg glitchRage glitch
Surf glitchTweakingPal Park Retire glitch
Generation V GlitchesBattle glitches
Charge Beam additional effect chance glitchCharge move replacement glitchChoice item lock glitch
Frozen Zoroark glitchSky Drop glitch
Generation VI GlitchesBattle glitches
Charge Beam additional effect chance glitchCharge move replacement glitchChoice item lock glitch
Lumiose City save glitchSymbiosis Eject Button glitchToxic sure-hit glitch
Generation VII GlitchesBattle glitches
Charge Beam additional effect chance glitchCharge move replacement glitchChoice item lock glitch
Toxic sure-hit glitchRollout storage glitch
Generation VIII Glitches
Charge Beam additional effect chance glitchCharge move replacement glitchChoice item lock glitch
Toxic sure-hit glitchRollout storage glitchParty item offset glitch
Generation IX Glitches
Glitch effects Game freezeGlitch battleGlitch song
Gen I only: Glitch screenTMTRAINER effectInverted sprites
Gen II only: Glitch dimension
Lists Glitches (GOTCG GBSpin-off)
Glitch Pokémon (Gen IGen IIGen IIIGen IVGen VGen VIGen VIIGen VIII)
Glitch moves (Gen I) • Glitch types (Gen IGen II)


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