I did eventually figure out the melee attack thing, but I'm still not able to get past the first level. I made it to level 3 by editing all the monster HP values to 1 but still died. :-(
The equation I can't solve is: melee attacks increase mana, but decrease HP, and enemies often seem to attack first even if I'm melee attacking them for their last hit point. It's only possible to increase HP using the darkness spell, which costs more mana than I get back when I kill an enemy. So I don't see how you could possibly run at an HP profit even when attacking weak enemies like slimes. And if you don't have any darkness essence at all, then it's impossible to regain HP, and you'll quickly be killed trying to melee attack things.