MapServer, a founding OSGeo projects, has been powering mapping systems since the mid 1990s. This talk gives an overview of the many features of MapServer that have been developed over the past 25 years, with a focus on advanced functionality that is not well-known as they deserve. Features will be shown using sample Mapfiles - the configuration files used by MapServer. Examples will include advanced symbology, special layer types such as graticules, charts, and contours, displaying data from S3 buckets, and more!