Interested in joining the Silph Research group? Learn More »

Silph Study: #054


Mythbusters Part 3: Event Decay

Welcome back, travelers!

Anyone who plays Pokémon GO on a regular basis is very familiar with how many events take place, and that events have become an increasingly big part of the game and how it functions. In the 11 months between the introduction of Seasons in December 2020 and the end of the Halloween 2021 event, there have been 232 event days. This equates to 69% of total gameplay, an increase over the 56% of gameplay filled by event days in the 11 months prior to Seasons. Many of these events have been subject to speculation about “event decay”, the idea that event spawns become less common near the end of an event. Could there be any truth to these rumors?

Myth: The frequency of event spawns reduces over time during an event.


This study looked at events that lasted for at least five days between March and September 2021, to allow ample time to compare the event spawn frequency from the start and end of each event.¹

Five of the 13 events studied show a marginal decrease in event spawns; however, we are unable to reject the null hypothesis that the proportion of event spawns at the start of the event is equal to the proportion of event spawns at the end of the event for the first 12 events in the chart (all Bonferroni-corrected p-values > 0.05). This means these minor fluctuations in event spawn frequency are most likely due to chance alone, rather than intentional game design. The thirteenth event offers an insight into what would happen if Niantic did make a concerted effort to alter the spawn rate of featured event Pokémon.

Bidoof Breakout

Bidoof Breakout was the only occasion where there was a significantly different spawn rate of the featured species between the start and end of the event (z = 9.5, Bonferroni-corrected p-value < 0.001).² In this instance, however, Niantic had stated in advance that the spawn rate would increase during the event. The change in frequency can be divided into three distinct levels corresponding to each special move period from the event, as shown in the table below.

Event Day Total Spawns Bidoof % Special Move Bidoof %
Day 1 160 21.9% Shadow Ball 21.3%
Day 2 178 20.8%
Day 3 185 31.6% Thunderbolt 29.2%
Day 4 209 27.3%
Day 5 188 63.3% Ice Beam 64.1%
Day 6 194 65.0%

This gives us a glimpse into how the frequency of event spawns could be changed when intended by the developer. Could we see this style of ramping event spawns for future announced events?

Parting Words

After analyzing event spawn frequency in over 20,000 spawns, we’re ready to call this myth:

One likely cause of the perceived decay in event spawns is the increasing familiarity of the spawns as the event progresses. When an event starts, the new spawns are exciting and unique, because they stand out from the same few species we see every day. By the end of the event, we become accustomed to seeing the featured Pokémon, so they stand out less from the seasonal spawns and may therefore seem less common.

Until the next myth we get to bust, stay safe, travelers!


Authors: Scientists PhoenixCrystal and Pancake
Analysts: Scientists Pancake and CaroKann
Project Leaders: Scientists Cham1nade, PhoenixCrystal, and Gustavobc
Graphic Artists: Scientists WoodWoseWulf and CaroKann
Editors: Senior Researcher JinianD


¹ The spawn frequency comparison looked at the first and last three days of each event. For events lasting less than six days, we considered the first and second halves to avoid overlapping spawns in the middle of the event.

² In further analysis, we looked at the event spawn rate every two days over the course of each event. We found minor fluctuations in event spawns that are likely attributed to sampling error. There was no significant overall change for any event except Bidoof Breakout.