I've heard that there are a lot of Nintendo references in the original game, some of them parodying Pokémon. The card company is called 'Nantendo' (and still is in the sequel); this joke actually originated in the Game Boy game For the Frog the Bell Tolls (also developed by Intelligent Systems) where Dr. Arewo Shitain (who curiously cameo'd as an enemy in Wario Land 4) is the owner of the Nantendo building on Nantendo Island. Secondly, Maruo Maruhige owns a card company, but it's said somewhere in the game that he used to be a taxi driver, where Nintendo used to be both a card and taxi company.
What interests me are the Pokémon parodies. There is apparently an NPC who calls "Team Pocket" as one of his favourite villains, (I'm not sure who though) and whereas everybody is obsessed with "Card Hero" there are a few NPCs who talk about another game called "Rocket Monsters". I'll try and grab a screenshot of one of these references.