The Replacement Project was an ongoing job of correcting and changing dragon sprites. It was originally set up to completely change all dragon sprites that were on the site at the time, which were all from various video games. Because of copyright issues, it was mandatory that they were replaced, and thus TJ09 and other artists started this project. The acting out of this part of the project is today known as The Great Fog or The Fog, in reference to the many days where all dragon sprites were temporarily fog sprites until they got their new sprites from the Sprite Replacement Project.
The project has since died down, as of 2012. After "The Fog", it was mostly used to change sprites which people didn't like or which are anatomically inaccurate. Once its own forum section, this has since been closed and removed on the forums. Today, there is much debate as to whether sprite updates should be occurring on-site and while they are rare, some sprites are still receiving updates as of 2015.