>>35785585Look at Vaporeon for example. Notice how it has frills, fins and a fish-like tail that give it the appearance of a mermaid and make it stand out among the other eeveelutions (which are much more bland and less creative design-wise). This is an example of what Eevee should look like when it evolves and adapts to its surrounding environment.
The concept of beta Leafeon is the essentially the same - unlike gen 4 Leafeon, beta Leafeon undergoes a complete transformation and truly adapts to a forest-like environment.