|The symbol for Delta Pokémon|
Delta Pokémon are a special kind of Pokémon whose type and appearance differs from their normal counterpart.
According to Professor Pine, Delta Pokémon are believed to originate from the Holon region, though the reason for their existence is unknown. The Perfection cult studies Delta Pokémon as a part of their goal to obtain the perfect Pokémon, since the group believes Delta Pokémon to be stronger than their regular counterparts. Experiments done by Perfection scientists are responsible for the creation of some of the Delta Pokémon that can be found in the Torren region.
Delta Pokémon are rare, typically only being found in in-game events.
Delta Pokémon can only breed with Delta Ditto, with the exception of Delta Ditto itself, which can breed with any Pokémon that is not in the Undiscovered Egg Group, or Ditto Egg Group. Additionally, Delta Pokémon whose non-Delta counterparts are in the Undiscovered Egg Group (Delta Pokémon whose base forms are baby, legendary, or mythical Pokémon) are unable to breed.
The weight of a Delta Pokémon is either equal to the base form's weight or equal to 0.5×, 1.5×, or 2× the base form's weight. With the exception of the Delta Bulbasaur and Delta Combee evolutionary lines, Delta Pokémon have the same gender ratio as their non-Delta counterparts. All properties of Delta Pokémon that are not mentioned in this section are the same as that of their non-Delta counterparts.