Step 1: Green Face!
This whole look is pretty simple.
Starting off your going to paint your face green!
Step 2: Wrinkles Everywhere!
You'll need to add A LOT of wrinkles EVERYWHERE! Forehead, eyes, cheeks, mouth, and chin.
Step 3: Add Shading.
Use light green for high lights, dark green for contouring and shadows and if necessary add a little black to deepen shadows.
Step 4: Details
Use black body paint to make your nose and chin look short and fat. On your nose be sure to blacken the bottom and give it a flat look and widen the sides. Also use black on the bottom of your face to 'fatten' it up a bit and kinda give it a sagging look. Then paint your neck black.