A small piece of cardboard with a cartoon Pikachu on it recently sold for $16.5 million.

The 1998 Pikachu Illustrator Pokémon card set a record earlier this year, CNBC reported. The seller was wrestler and influencer Logan Paul, who paid $5.3 million plus a trade for it in 2021. That beat the $12.6 million paid in 2022 for a famous 1952 Topps Mickey Mantle baseball card.

Those are extreme examples. But trading card games, led by Pokémon, Magic: The Gathering and Yu-Gi-Oh!, are becoming a popular investment, CNBC said.

"It is one of our fastest-growing categories," said Adam Ireland, who runs collectibles at eBay. "From an investment point of view, you start with Pokémon." It was the most searched term in eBay's collectibles section in the first half of the year.

Heritage Auctions started a trading card department six years ago. "Now it's a $50-million category," said executive Joe Maddalena.

Grading, scarcity and authentication can decide whether a card is worth a few dollars or hundreds of thousands, CNBC reported. Grading companies inspect cards and give them a score, usually from 1 to 10. A perfect 10 can be worth many times more than the same card in worse shape.

The Pokémon card game launched in Japan in 1996, making it about 30 years old, AOL noted. That makes it young compared with many collectibles.

Experts warn that prices can swing a lot. They advise buying cards you enjoy, checking for fakes, and not putting money you need into collectibles.

What we know: graded rare cards can sell for high prices.
What we don't: whether today's prices will hold.