Today, the Pokémon Essentials wikia and all downloads for it have been taken down due to a copyright claim by Nintendo of America.
Nintendo has been on a 'warpath' recently, first going after ROM sites, and now they back to going after 'fan-made' games, finally setting their sights on 'Pokemon Essentials' after it being free from any 'strikes' by Nintendo for over a decade, but that is no longer the case, as of today all downloads have been removed, but existing mods which don't feature 'Essentials' itself will still be allowed.
In the official announcement link below, they state not to get totally 'freak' over it all, and not to 'get angry' or make a 'big deal' about it.
OFFICIAL SOURCE: --> https://www.pokecommunity.com/announcement.php?s=5af0ff9955fa69681e879782cd7adaa8&f=244&a=823
NEWS SOURCE: Nintendo shuts down decade old fan game creation tool Pokemon Essentials (via) GBATemp