Use adobe capture on any mobile device to create a vector to import into PS. This will smooth out any jagged edges. Create a layer in PS and drop onto the canvas from your creative cloud vector library. Rasterize the layer. Create layers for each object in the drawing and use various brushes to create the look you desire.
In this case, I used a splatter brush for the leaves. add jitter for hue, position and brightness. I used a fan brush with some hue jitter and direction and used a bit of purity control. the trunk has another type of splatter brush applied. The serpent uses some emboss, and gradient overlay.
colored the rest with airbrush. then dodge and burn tool used to highlight areas I felt needed some depth and interest.
for a final touch I created a new layer using a flattened copy of the entire image. I then used an interpolation filter to give it an older paper look.