Extract the snowboarder by pen

Choose the bottom part of the source image, then spread it to have a mountain-like view. (Hide the layer of the snowboarder)

Lens blur and increase the brightness of the up-right corner (keep the border smooth by the feather of 100)

After some rounds of blurring and brightening, a desaturate step was apply to the whole background image

Bring back the snowboarder. Rotate, resize it to be small enough. Cut out the unnecessary board.

Duplicate the snowboarder layer to make his "brother". Select the coat and change the hue, saturation to make the blue coat. Also, resize and rotate this layer a little bit to make the difference.

Choose the right leg of both the red snowboarder and the blue snowboarder, flip horizontally and resize, rotate them, then join back the body to make it looked real

Use clone, eraser, brush, dodge with low opacity to modify the blue coat to make it looked different from the red one.

Make the shadow from the left to the upright direction, under the layers of snowboarders. Use pen, black coloring, Gaussian blur and reduce opacity, erase slightly the top of shadow. Also, make the shadow of the red snowboarder on the blue snowboarder. After finishing, apply Gaussian blur (radius 1px) to the snowboarder layers to fit them to the background.

Because these snowboarders are walking through the snow, they left their footprints and perturbed the place they walked over. Use the clone (low opacity), take the pattern around to make the plowed-like area. I also embedded a part of the board near the bottom of the image. Notice to make the snow around their legs.

Make a upper layer, use white spatter brush to make scatter clump (low opacity) of flying snow, then apply the moving blur to make the snow in the wind. Make some other layers with the same manipulation (change the moving direction a little bit and use grayer brush). Also, make the shallow DOF like the tilt-shift photography to make the photo more impressive. Finally, change the curve to gain the higher contrast.
PS: this is the remade SBS of my submission because I lost my psd file, so the last one is not the same as the one I submitted.