Rockfalls are natural phenomena that involve the detachment of a rock mass from a cliff or steep slope, followed by its downslope propagation. The initial volume can be large, which is referred to as a rock avalanche. However, in most cases, fragmentation occurs either at the source or due to successive impacts, making it possible to study the phenomenon as the propagation of multiple rock blocks. This process poses significant risks to infrastructure and human safety. Traditional 2D visualization methods often fail to effectively convey the complexity of these phenomena to stakeholders and end users (engineers, experts, authorities, communities, and students). Hence, the use of immersive 3D visualization with Mixed Reality is a powerful tool to overcome this drawback. This study presents the development of two Mixed Reality applications for HoloLens 2 using Unity Game Development Software to visualize numerical simulation of 3D rockfall trajectories over digital terrain models. The simulations were carried out using the RockGIS code, which include, the fragmentation of the original rock block. Two real-world case studies, Vallirana quarry real scale tests and a rock block in the Montserrat massif in Barcelona (Spain), have been used to demonstrate the improvement of spatial cognition and better understanding of rockfall dynamics and its associated hazard.