2020 has been the year of big Pokémon source code leaks, and the latest classic pair added to the list are none other than the fourth generation of games, Pokémon Diamond and Pearl. And according to fans who have perused the code, the 2006 pocket monster games pay special attention to what day it is.Twitter user @shinyhunter_map a Pokémon speedrunner and shiny hunter recently made a discovery that Pokémon Diamond and Pearl behave slightly differently on certain in-game days. On Pokémon developer Junichi Masudas birthday, which lands on Jan. 12, for instance, any eggs you try to hatch will grow 10% quicker than they usually would. The egg detail has been corroborated by Mr.Cheeze, another well-known Pokemon tinkerer. Its also worth noting that Masuda himself has coyly encouraged players to turn on the game on that date, promising that something different will happen. There's been a new, surprising discovery in the Gen 4 source found by @shinyhunter_map!On certain special days of the year, such as Masuda's birthday, Eggs will hatch 10% faster from normal.Doesn't look like this has ever been noticed before. I wonder if later gens have this? pic.twitter.com/AeI7mV9Rlm 87Ne (@MrCheeze_) May 27, 2020Thats not all. On certain holidays, like Independence Day (July 4) or St. Patricks Day (March 17), the games will also increase monster encounter rates by 5%. You can view the full list of holidays below:But Game Freak apparently didnt stop there. Surprisingly, the Japanese studio allegedly also alters monster spawn rates on tragic anniversaries, such as 9/11 or the day of the Hiroshima bombings.Reportedly, spawn rates are also lower on Christmas and New Years Day but only by 5%.Polygon cannot independently confirm the existence of this code. However, the code was also verified to Polygon by another known speedrunner, data miner, and hacker, Orcastraw, and has been shared by hackers with proven track records, like MrCheeze. Polygon reached out to Nintendo and The Pokémon Company to confirm the reports, and will update if the companies respond. Shinyhunter_map tells Polygon that they were able to look at the code through the DeSmuME emulator, a tool that allows users to peek behind the curtain.But the bigger question remains, why would Game Freak do something like this? Its hard to say, but hackers have theories. Orcastraw notes that Diamond and Pearl include something called a Pokétch, a watch with a true-to-calendar clock. Diamond and Pearl use this feature in more obvious ways, like having days where snow transforms into in-game diamonds. Theres also small, subtle things, Orcastraw told Polygon over Twitter messages. Theres one area called Valor Lakefront in Diamond & Pearl that has a small, rare amount of days itll rain, determined each year, and theres just an amount of clock based secrets hidden around that it makes sense theyd do something like this, she continued. According to Orcastraw, the spawn changes arent carried over to more modern games, however.Time-based mechanics are something that Pokémon has toyed with more broadly through things like day/night cycles. Pokémon Go, meanwhile, frequently increases spawns for certain monsters depending on the seasonal event. But observing mournful dates might just be the most experimental use of the idea yet.