You have to implement a 3D collision system yourself, C3 does not have support for this. I have seen and implemented examples of using collision filtering based on zElevation. More complex is to use a 3d collision JS library like cannon.js or simpler AABB bounding box collision in JS or C3 events. JS implementation is described here: https://developer.mozilla.org/en-US/docs/Games/Techniques/3D_collision_detection