I came across this 1999 'gem' at a consignment sale yesterday. The game itself is very blah/broken/luck-based. However, the card designs are amazing and with no text on the cards whatsoever! The size is nearly identical to the NA version of HeroQuest cards (minus a couple MM from one side perhaps). With sleeving these, you could use the "front" as the back and print out a custom card to slip on the new front to create new decks of cards for HeroQuest.
From the link below you can see the pics of the various cards - you get 80 in the game and with the exception of a few special cards, the 6 key groupings are in abundance.
https://www.boardgamegeek.com/boardgame/610/knights-rainbow/images
New spell schools, treasure deck, modifier cards for the fighter, etc. The possibilities are of course endless. This might be a good alternative for those who are looking to create a deck of cards but don't want to professionally print them just yet. A quick way to proxy them up and have some cool designs too!