The next mainline Magic the Gathering set is The Lost Caverns of Ixalan, taking place in the adventurous world of dinosaurs, pirates, merfolk, and vampires that is Ixalan. After the Phyrexian invasion of March of the Machine, the powers of Ixalan are scrambling to reach the center of Ixalan and explore the underground world that exists underneath the plane, inhabited by the enigmatic Oltec. As the third set on the plane of Ixalan, Lost Caverns has a lot to live up to in terms of developing and expanding the world we have already seen in Ixalan and Rivals of Ixalan.
Source:https://www.cbr.com/mtg-lost-caverns-of-ixalan-spoilers-previews/