The private equity firm that is buying and renting homes en masse all over the country has also just bought one of the most popular Pokémon card grading companies. The deal valued the grading company at more than $500 million. Highly graded rare Pokémon cards can fetch thousands or tens of thousands of dollars on the secondary market. It authenticates coins, grades comic books, throws various industry events, and, about a year ago, started grading Pokémon, Magic the Gathering, and Yu-Gi-Oh cards. Blackstone is now, perhaps bizarrely, adding a card grading company to its portfolio.