Pokémon δ are Pokémon with unusual typing, found only in the Holon region. Metal hybrids -- for example, a water-type becoming water/steel-type -- are the most common type of Pokémon δ, although it's possible for any mutation to occur.
Any foreign Pokémon that comes out of its Pokéball in Holon has a chance of mutating. The only Pokémon who are immune to delta rays are the species native to Holon -- Magnemine, Magneton, Magnezone, Voltorb, Electrode, Nosepass, Probopass, and Castform.
Any foreign Pokémon that comes out of its Pokéball in Holon has a chance of mutating. The only Pokémon who are immune to delta rays are the species native to Holon -- Magnemine, Magneton, Magnezone, Voltorb, Electrode, Nosepass, Probopass, and Castform.