Ditto is a Normal-type Pokémon which has the ability to change its form to mimic other Pokémon species. In Pokémon GO, it cannot be directly seen in the overworld map but it is still obtainable by catching. Due to its unique ability, it was not released in the game until November of 2016.
Taking its abysmal base stats into consideration, it’s no wonder that Ditto isn’t a meta-relevant Pokémon whatsoever. Despite this, its in-game mechanics are so unique that it’s interesting enough to be worth discussing.
Ditto can disguise itself as the following Pokémon, and will reveal itself once the Pokémon is caught. Ditto is noted to have a low Base Catch Rate (20%) compared to the Pokémon it can be disguised as, and is far more difficult to catch. If that Pidgey’s popped out of five Pokéballs already, you might have a Ditto on your hands!
The color of the disguised Ditto’s target circle will not reflect its actual catch rate, but that of the species it is mimicking.
The encounter CP will most likely change when it is caught, as the CP of the disguised Ditto reflects the stats of the species it is mimicking. The Ditto’s level will not change once it is caught, although the CP now reflects Ditto’s own stats. Being Normal-type, it receives a weather boost in Partly Cloudy weather.
Once the Ditto disguised as one of these Pokémon is caught, an “Oh?” will appear above the Pokéball (where “Gotcha!” normally would), followed by a short animation of Ditto revealing itself. Ditto can be caught with a Go Plus, and if the disguise Pokémon is shiny on the encounter screen (only Shiny Magikarp from the above list is currently available), Ditto, unfortunately, will not be shiny.
Additionally, Ditto is not individual as shinies are — a Pokémon will be Ditto for anyone who catches it.
Battling with Ditto
All Ditto will have the quick move Transform and the charge move Struggle. As soon as the battle begins, the attacking Ditto will transform into its first opponent (and retain this form throughout the battle) regardless of whether or not the player is tapping to activate the quick move.
Once Ditto transforms, it takes on the Attack and Defense stats of the opposing Pokémon, as well as its moves and typing. Its Individual Values (IV’s), HP stat, and level will remain the same. Because of this, a Ditto’s CP often increases drastically when battling powerful opponents such as Dragonite.
Ditto is not a recommended choice for any matchup. Although it can transform into powerful Pokémon, its low HP stat which remains constant makes it a glass cannon in any role. If absolutely necessary, a defending Ditto is best countered with Chansey; it will transform into a Pokémon with poor attack and defense stats, and although Chansey has an overwhelming amount of HP, Ditto cannot mimic it.