He's jumping in celebration in the last picture, something like this:
Joy is an emotion too you know. Mario doesn't need to be accompanied a story of Shakespearean proportion. We just need a basic reason to go through multiple levels.
Now you're talking. Yes, joy is an emotion, that's for sure, but it's best lived in balance with other emotions. If I were to desing a joyful Mario, I would make sure to not cause that joy to be the sole emotion felt.
Joy is one of those emotions that is best brought to life by hardships or when faced with a threat or an ennemy. As such moments of joy only then take their full meaning.
The feeling of threat and urgency is very poorly portrayed in Mario, and the joy being so omni-present really drowns out any other emotion.
Though you can understand my appreciation for the emotion that joy is, the pictures you gave, a person, in the sunset, wearing a hoody, and just enjoying the nature around him, paints a very different picture from the overly bright worlds of Mario, especially the latest incarnations.
Lastly, in my opinion, joy is most often experienced within, with the outward expression of that in most cases being an unforced expression that doesn't necessarily involved shouts of joy. Joy can often be espoused with serenity.
But that's a good post. Thanks.