I stumbled upon this concept when sketching out lions crossed with fruits, when I realized that dandelions are a plant with fanciful-looking seeds, and a dandy is a fancy person. A dandy lion fits very naturally with Grass/Fairy, so I went for it!
I added a few other design elements to mesh concepts together. The dandelion puffs form the dandy lion's fluff. The lion's dewclaws give the impression of cufflinks. A boutonniere is a great grassy and fairy-like addition to a fancy feline's ensemble. As "dandelion" originates from "lion's tooth", the lion has cute little fangs. :P
I made sure dandy lion was a sunny creature. Lions, in contrast to other big cats, are active during the day. Additionally, they live in the savannah, a temperate region between a forest and desert. The eyes on the design are colored like the
desert dandelion, which are yellow with a red center. In general, dandelion flowers invoke sun imagery.
This design also fits the expected weight criterion for this CAP. As S. Court points out,
big cats can reach 418 kg, which is perfect on dandy lion for reducing damage taken from bamboo rocket ships. You can imagine dandy lion as more massive, even, given Pokemon's propensity for exaggerating units of measurement.