Mario Super Sluggers Cards was an online card game created to coincide with the release of the Mario Super Sluggers video game in North America in August 2008. The game was available on mariosupersluggerscards.com and the cards to collect for it were found on kid-friendly sites like 4KidsTV, Nick.com, and YouTube. The main materials on the site included cards of each character, each captain's Star Swing and Star Pitch, each team, and the five default stadiums.
Players could do many things with their cards, such as swapping them with other users. It was discovered that it was possible to clone cards by swapping with themselves and accepting the swap. As users obtained more character profile cards, they were also able to choose icons of available Mario Super Sluggers characters. While on the site, Lakitu gave the users hints from time to time about their collections.
The cards were categorized by their respective levels. Level 1 cards included the forty-one characters available in the game, with alternate colors excluded. Level 2 featured the Star Swing/Star Pitch of every Team Captain, and they were made by making double plays with Level 1 cards. Level 3 included cards of each team in the game, and they were made by making double plays with Level 2 cards. Level 4 featured the five stadiums that do not need to be unlocked, and they were made by making double plays with Level 3 cards. Luigi's Mansion, Daisy Cruiser, Bowser Castle, and Bowser Jr's Playroom were the only stadiums that did not appear as cards in the collection.
If a user completed their Mario Super Sluggers card collection, they were able to receive a poster download featuring Mario and all the cards that they had collected. The Mario Super Sluggers card game has since ended, and the site is no longer available.