Types have been the main basis of the battle aspect of Pokémon since the very beginning. With 18 different types with dozens of Pokémon in each type with dozens of attacks of each type. All Pokémon have set types but this is not always the case. While Castform, Arceus, Shaymin, Rotom, Darmanitan & Meloetta have different types based on forms, there are other ways to change the type of the Pokémon.
There are various moves and abilities which can remove immunities based upon the Pokémon's type combinations and some which boost stats, but there are a handful of attacks and abilities which can alter the Pokémon's type. To top that off, Black & White introduced a means in order to change your opponent's type to a specific type.
Pokémon Type Changing
The move Soak is a relatively simple move. With it, you can take your opponent and submerse them in water, thus making them a pure Water-type, removing all of their type combinations and immunities. It also removes any Same-Type-Attack-Bonus they would have received from the moves in their moveset. This will allow you to fully hit in with Grass & Electric-type moves to damage the opponent.
The move Forest's Curse is a relatively simple move. With it, you curse the Pokémon and add the Grass-type to them. This will make Single typed Pokémon Dual-typed and Dual-typed Pokémon Triple-typed. As such, the Pokémon's type calculations will be altered. The Pokémon gains all the benefits and hinderances of the Grass-type, including immunity to Leech Seed, Grass-type STAB and the various other bonuses. It fails if the target is already Grass-type
The move Trick-or-Treat works identically to the Forest's Curse move. With it, you curse the Pokémon and add the Ghost-type to them. This will make Single typed Pokémon Dual-typed and Dual-typed Pokémon Triple-typed. As such, the Pokémon's type calculations will be altered. The Pokémon gains all the benefits and hinderances of the Ghost-type, including ability to retreat from battle if restricted by an ability, and immunity to Normal and Fighting-type moves. It fails if the target is already Ghost-type
Burn Up is a move introduced in Sun & Moon with an interesting twist. While it is a powerful Fire-type move, when a Pokémon uses it they will lose their Fire-type. This means if they're dual-typed, they'd become single type. If they are pure Fire-type normally, they will then become typeless with no weaknesses. This effect is removed on switch out and the move will fail if it is used by a Pokémon that is not a Fire-type, including those that are now typeless.
Camouflage was originally a Staryu only move, but has since been learned by various other Pokémon. Camouflage will change the type of the user to a type depending upon the terrain in which it battles. In-game, this is highly useful. However, in the WiFi Rooms, it is rather limited as it will always be within a building. The places and types are as follows
Conversion is a move introduced within the first generation and thus the first move which actually changed the type of the Pokémon. Conversion changes the user's type to the type of the first of its four moves. This will allow you to get the Same-Type-Attack-Bonus from these moves. However, as you don't have control over it, it will be completely random.
Conversion2 is a move which was introduced in the second generation to randomly change the type of the user. Unlike the above move, the type the user becomes varies. The user will become a type resistant to the type of the move that hit it so if it got hit by an Electric-type move, it may become a Ground-type. However, it can't make the user the same type as it already is, so if that would occur, the move will fail. Click here to consult with our Type Chart
Reflect Type is a move introduced within Generation V which allows for the user to take the complete type of the target Pokémon. This includes both types so can turn Mew from a Psychic Pokémon to a Dragon/Fire if it's against Reshiram or basically any type it is battling against. This can also be done Double & Triple Battles, by targetting your allies instead of your opponent, that way your Pokémon shall receive their type.
Color Change is a simple ability known only by Kecleon. This ability will change Kecleon's type to the type of the move that previously hit it. This gives Kecleon a tactical advantage against Pokémon who use single type moves. In Generations III & IV, this ability changed Kecleon's type with each hit on multi-hit moves, but with Black & White, this was removed and Kecleon only changes type after the final hit has occured.
Protean is a new ability that is able to be had by Kecleon, Froakie, Frogadier. This ability will change the type of the Pokémon into the type of the move it is using, just before it uses it. This makes it a pure Pokémon of that type, and gives it STAB from the moves it uses. It also messed with any strategy that the opponent may have.
Multi-type & RKS System
Arceus' Multitype and Silvally's RKS System ability allows for it to change its type based upon its hold item. Throughout the games, you will find 17 different kind of plates and Memories. Attach these plates to Arceus & Silvally and its type will change to the respective type for however long it holds onto this item.
Attack Type Changing
In addition to Pokémon changing their type, there are various moves and abilities that can change the type of moves used by other Pokémon.
Electrify is a move known by a few Pokémon that targets the opponent. If the Pokémon it is used on attacks after it has been hit by this move, its move becomes Electric-type and susceptable to all resistances including Lightningrod in Double Battles.
Ion Deluge is a move known by a few Pokémon that targets the entire field. When in effect, it turns all Normal-type moves into the Electric-type.
Judgment & RKS System
The move Judgment is known by Arceus and, like Arceus, will change its type to the type of the plate that is attached to it..
Revelation Dance is a move that changes type based on the type of the Pokémon using it. It can only be used by Oricorio but changes based on its form so it can be Electric, Fire, Psychic and Ghost.
The move Weather Ball is an adaptable move that changes its type based upon the current weather effect. If Sunny Day, it becomes Fire-type. If Rain Dance is in effect, it becomes Water-type. If Hail is in effect, it becomes Ice-type and if Sandstorm is in effect, it becomes Rock-type. Its power is also doubled.
There are also several abilities in the game that will change the type of certain moves used by it. This allows for them to receive STAB for the move, as well work into the strategies. Abilities such as Mold Breaker do not affect them, however once a Pokémon loses its ability, it loses the change.
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