I started off with a sphere I modified, so it looked balloonish and added a spline with sweep nurbs and a circle.
step 2 of 8
I used a hemisphere as base model for the hat.
step 3 of 8
Modelling details...
step 4 of 8
more details...
step 5 of 8
details...
step 6 of 8
After I added hypernurbs, I made the object editable and added hair.
step 7 of 8
In the end I started designing the environment.
HDRI background is a preset in Cinema4D.
I played around with different things.
In the end I decided to go with the forest and added some bubbles with the emitter (simple spheres).
I also added a foreground vignette (simple circular gradient alpha) and glow as a post effect.
step 8 of 8
Finish: Levels and channel contrasts were adjusted.
(This pic shows an earlier render stage.)