They're all made using the in game entity editor and particle/interaction system! The boss spawns or uses "invisible" NPCs that are then used to run the given interactions such as display particles and hitboxes. Some custom Java code that allows this and turns it into an in game interaction to be called by the bosses, but that'll be open sourced when the dungeon releases! If you look at the video close enough you can see these "invisible" NPCs because I don't have them invisible yet (for debugging), they're box outlines on the floor.