The fourth scene shows a body-builder running in a rough terrain.
The terrain was created by subdiving a plane and giving it a displace modifier with a noise texture.
Unfortunately, it is not possible to use the Keep Feet Above Floor tool, because it only acts on the object location and rotation. Instead a second animation layer was created with the Start Edit button. For multiple keyframes, the root (hips) bone was moved in the Z direction to make the foot rest on the ground, and a keyframe was inserted with the Loc button. The animation was baked several times with the Confirm Edit button, and the process was repeated until an acceptable result was achieved.
It is a good idea to often bake the animation layer with Confirm Edit, and to create a new one with Start Edit again. Blender can become unstable if one works with an animation layer for a long time, and a crash would mean that much work is lost.
I did not have the energy to perfect the animation. E.g. at frame 109 the right foot penetrates the ground, which is most easily seen from below (although it is only what can be seen from the camera view counts). Although the problem is apparent in a still photo, it is not so easy to notice in an animation.