What do you get when you form a partnership between the blue chips at American Express and a company called Riot Games?

A prepaid debit card aimed at the millions of 18- to 24-year-olds who are dedicated players of the wildly popular "League of Legends" online video game.

In case your kids haven't told you, "League of Legends" was created by Riot Games in 2009. It's part of a gaming genre in which participants compete against each other in tournaments that are streamed online. The games can be played for free, but players must buy what are called Riot Points to gain access to specific features or characters to advance their gamesmanship.

That's where the "League of Legends" Amex Prepaid Card comes in.

American Express rolled out the card in mid-August with the motive of making banking inroads with the millennial generation of teens and young adults. A company executive cited 32 million decidedly male gamers worldwide who play "League of Legends" a "staggering" 1 billion hours a month as a reason for partnering with Riot Games. That's a lot of potential American Express customers.

Riot Games, in turn, is splashing promotions for the card on its website and hopes to reap enough financial rewards from the American Express sponsorship to help pay for the high costs of promoting the game to a wider audience.

Prepaid cards, which act like debit cards, have become popular alternatives to traditional bank accounts and credit cards, especially for millennials. You load the card with a fixed amount of money and use it instead of cash to make purchases. Once the money is gone, you can't use the card until you feed it more cash.

American Express offers six customized "League of Legends" cards, including plastic emblazoned with champion characters such as Twisted Fate, Teemo and Lux, or the game's logo.

Users earn 1,000 Riot Points when signing up for the card and an additional 1,000 game points when loading at least an initial $20 onto the card. More points are earned after the first 10 purchases with the card, and players who use direct deposit to transfer funds, say from a paycheck to the prepaid card, earn 10,000 points.

I've never been a big fan of prepaid cards because many of them charge excessive fees that can eat up a chunk of a cardholder's money. But American Express said the "League of Legends" product has only one fee -- a $2 charge for cash withdrawals outside the financial service company's ATM network. There are no activation fees, credit background checks or minimum balances required.

I asked two bank card experts to critique the "League of Legends" product and both gave it good marks, mainly because of the low-fee plan.

But as a parent, one thing bothers me: linking Riot Point incentives to swiping the plastic. Games can become very addictive, and that could turn out to be very costly.

Only you and your gamer will know whether there's reason for concern about money misadventures. The other important thing to remember, however, is that the card can be a useful financial tool. Just use it wisely if you want to stay in the game.

(Questions, comments, column ideas? Send an e-mail to srosen(AT)kcstar.com or write to him at The Kansas City Star, 1729 Grand Blvd., Kansas City, MO 64108.)