Henriquejr spotted an Master of Magic update and a DLC on GOG:
More information.Master of Magic gets an update and new DLC from Slitherine
The classic strategy game receives a new version with fresh features and visuals. Master of Magic is now available on GOG.COM in a completely updated version.
Also, you can now acquire a Master of Magic: Caster of Magic DLC that further expands the game's universe and the community options.