As previously covered by the Silph Research Group, Special Lure Modules such as Magnetic, Mossy and Glacial Lures will summon a roughly 50/50 mix of a limited number of predetermined lure-type-specific Pokémon species and Pokémon species from the local biome. After careful analysis of observed spawn rates from all types of lures currently available in Pokémon GO, Silph Researchers have discovered an additional phenomenon that occurs only when Magnetic, Mossy or Glacial Lures are active.
Bias Towards Pokémon With a Higher Pokédex Number
The following figure includes data gathered from 324 normal Lure Modules, 271 Glacial Modules, 145 Magnetic Modules, and 174 Mossy Modules between May 2019 and April 2020. The 13 Pokémon species that are known to spawn as a result of each particular Special Lure’s elemental effect were removed prior to rendering. Lure data collected during special events which boosted any of the known 13 predetermined species attracted to each kind of Special Lure Module was also not included.
Based on our previous understanding of Special Lure Modules, the remaining 50% of spawns should match a normal Lure Module, however, what we observe from all Special Lure Modules is a strong apparent bias towards biome-native Pokémon that occur later in the Pokédex. In contrast, Pokémon summoned by normal Lure Modules appear to display no such bias. The few observed species below Pokédex number ~190 from Special Lure Modules are a mixture of event-boosted species, possible reporting errors, as well as a small handful of verified examples where a Kanto species was drawn to the Lure.
Discussion and Implications
At this time, we are unsure of why this bias occurs, there are some interesting parallels that can be drawn with the Nest Masking phenomenon  that has also been observed to limit or block Pokémon species with low Pokédex numbers in parks and other areas in favor of the nesting species. Further, it is hard to say whether this is a bug or a feature, or whether Niantic is aware or concerned that this masking occurs in cases such as this.
While this bias makes for an interesting observation that could potentially lead to future discoveries, at this time we can only speculate as to why it occurs. The bias observed in elemental lures does, however, add further weight to the hypothesis that Pokédex order plays an important role in Niantic’s spawn generating algorithms and biome related databases. The Silph Research Group will continue to work to understand these mysteries – until next time, see you on the road!
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