Karina Longworth delivers the best post mortem analysis that I've yet read of the disaster that was Super Mario Bros.: The Movie:

As per usual, the kids of America proved the critics wrong: They were neither rabid nor traumatized, just indifferent. The film opened Memorial Day weekend on 2,000 screens in the U.S. — about as wide as releases got in those days. Its $8.5 million debut take was good enough for fourth place, behind Cliffhanger, Made in America, and (in its fourth weekend) Dave. Super Mario topped out at just less than $21 million domestically. Given the cost of the production and the confidence in the property, by no metric could this be seen as anything less than a failure.