The exact conditions which produce a given Type of Delta vary dramatically. The Delta phenomenon was first recorded during explorations into the Holon Region, an area rife with unusual electromagnetic storms and similar events, as well as strange crystal formations.

Many of the Moemon in that region were found to have unusual types, particularly Electric, Steel, Fighting, Dark, and Psychic.

However, other Typical Anomalies were observed, such as Water, Normal, and even Grass.

Studies have eventually led researchers to believe that there are two primary factors in producing Typical Anomalies, and therefore Delta Moemon. The first condition that seems to influence Type appears to be the conditions of the environment.