This is because of its Poison Peak ability, which allows you to put an extra two damage counters on your opponents Pokemon during Pokemon Checkup
Whats more, it creates 1/1 Human tokens, so you can have a human typal subtheme, preferably with gold cards
Glimpse of Nature is probably the most powerful card among these, easily enabling broken starts to Badgermole Cub decks, but that archetype isnt really an issue in Historic at the moment
They're the genuine first English Pokmon cards distributed publicly, predating Base Set boosters by roughly a month
Credit: Wizards of the Coast Muddle the Mixture Muddle is a decent counterspell but only for winning interaction wars, but what makes it top tier is transmute, letting you grab a 2 cost piece you really need, without even casting a tutor, so it's generally uncounterable
A non-terminal repeating phantasm, or a Class Five full-roaming vapor, is haunting Secret Lair