Saw this note you left on NintendoAge:
with casper instead of it saying Nasume it says Laguna
If it's Laguna, Laguna was a publishing arm in Europe, so it's likely that you have a European copy...
Screenshot would still help though.
IF I had to venture a guess, you likely have a prototype of the KSS version of Casper that was destined for Europe. Here are the differences between the two versions:
http://gaming.wikia.com/wiki/CasperKSS version
A different game was released only in Japan by the anime company KSS. In this version, the game uses an isometric view and the player controls Kat Harvey herself as she protects Casper from a duo that consists of a male government agent and a female government agent. During the course of the game, Kat collects items, therefore making this game an adventure game as opposed to an action game.
Baseballs are used to stun the secret agents. Getting hit by a secret agent results in a game over. There is even a box to the bottom right that keeps track of time (in seconds and minutes); the game starts with ten seconds elapsed. Saving the game is as easy is finding mechanical contraptions and activating them. While saving the game, the game counts all the coins and gems; it uses that count to tabulate a percentage to decide how much of the game has been officially completed.
Worth noting to see if you have an unreleased PAL version of the KSS copy.