how can I create footprints in the sand in an easy way
Sculpt it. You don’t even have to use Zbrush, Maya has some sculpting tools that can be good for that purpose.
Yogev is right you can also just paint a displacement in photoshop.
Or you could take a foot from a 3D model substract it from the surface then “smudge” the polygons a bit out?
Autodesk showed some Bifrost magic at FMX. I hope the video goes online soon.