hormondan
Hormondan is a fictional element appearing in DC Comics, primarily associated with the planet Daxam and its inhabitants. It is a rare and highly potent substance that is toxic to Kryptonians, rendering them vulnerable and eventually fatal if exposed. While Daxamites themselves are immune to its effects, it serves as a significant weakness for Superman and other Kryptonians who have settled on Daxam.
The element's properties were established to explain why Kryptonians like Lar Gand (Mon-El) and other Daxamites
The discovery and understanding of Hormondan have been crucial plot points in various Superman and Legion