So, as you know by now, the Mind Melt spell is "impossible" to get in the patched version 1.02 of the game. This is the version GoG has, as well as the free abandonware version from before that. And (I think) the CD version - basically everything except the original floppy version.
This spell was ONLY available by completing a mini-quest in Dencamp on the Teeth. In one house, a "red haired" guy gives you a password to tell the guard house just north of him. It's the wrong password, though. Originally, you go back to him, intimidate him, and he gives you the correct password - "diamond". Unfortunately, for some reason, in version 1.02 - the only version you will ever play, most likely - he is no longer at the house, and you cannot get he correct password, thus you can never finish this quest or get the "Mind Melt" spell. EVER.
This is a great spell, so I messed around with the hex a little and figured out how to fix/advance the quest REALLY simply.
After you start the quest, and are told "golden treasure" is the wrong password, make a save. Then, open it with any simple hex editor. I used HxD. Go to line (or "offset") AC0 (listed as "00000AC0"). The 6th digit will be a "4" (so, like, xx xx x4 xx xx xx xx xx xx xx xx xx xx xx xx xx will be the full line). Just change the "4" to a "C". Save the file. Exit. That's all. Just load your game, and go talk to the guy now. He will give you the right password and allow you to finish the quest and get the spell.
I wish I knew how to make a .exe patch file you would simply run on your save file to change this one hex digit, but I have no clue lol. So good luck! And have fun