How do I make a hero steal money from the enemy?
There is no built-in feature to steal money from an enemy, but you can simulate this effect by making an attack that "costs" a negative amount of money.
First, create a stealing attack. Give it a name and a description
In the Cost menu set the gold cost to an amount like -20 or -30 (depends on how much you want to win)
A disadvantage of this method is that it always steals the same amount of money from any enemy. One way to work around this would be to make several different versions of the stealing attack, and make the better ones only work on certain enemy types (using the fail vs enemy type bitsets)
This "stealing" attack will not reduce the amount of gold that the enemy drops when they die.