This is about the anime characters. For the monster itself, see Hopper.
Hoppers are small lemur-like monsters in the games, but their design is far more cat-like in the anime series (although it retains its lemur appearance in the anime-based card game). In its fight against Mocchi, Hopper uses its large paws and sharp claws, instead of the famous boxing and kicking moves that it has in the games. It also has very pointed ears in the anime.
The Searchers meet a Hopper in Episode 66 of the anime series, as one of Nina's monster companions (the other being Gray Wolf after he is reborn). Together, the three of them plan to win the Legend Cup. In Episode 50, two Hoppers are holding the prize money for the champions of the Legend Cup tournament.