Popplio when standing on its fins bears some resemblance to the alchemical symbol of mercury (representing Water).
Popplio gained notoriety when an alleged leak of its final evolution depicted a creepy-looking circus clown seal which earned Popplio much negative opinion on the internet. Fortunately, the reveal of its beautiful mermaid-like evolution Primarina brought it back to fanbase popularity.
Popplio is based on a sea lion and the Hawaiian monk seal. It is also based on the classic depiction of a circus performing seal, with the collar around its neck and balancing a ball, or bubble, on its nose.
Popplio is a combination of pop (as in popping bubbles) and lio, the first three letters of lion in sea lion.