Being an ability helps, too, since you never have to put it on the bench or give it any energy to get its effects, leaving you to do the poisoning with better Pokmon in the active spot
Beyond that, the set is littered with big-ticket chase cards, such as a secret alternate art version of beloved dragon-type legendary Rayquaza as well as more Eeveelutions with secret alternate art in the form of Leafeon, Glaceon and Sylveon.
Hes fragile to board wipes, but with counterspell backup, he can pressure opponents by sheer numbers
In the specific case of this card, the English version is a bigger catch than the Japanese
In any case, these one-use flicker cards almost never do anything else to impact the game, so increasing their density to have access to them all the time is filling your deck up with situationally-useless cards