Thanks!
The player should not controll it, because it is a kind of Berserk. Some creatures of the Bastion town can cast this "Berserk" on enemies, and they will attack only them. During tests it does not matter which stack you attack, you can try to do it with your own stacks (for example, with the stack 0). In my code I get the stack ID this way:

I had some Ideas, but I could not finish this work... You need to find a reachable position nearly the target, than set it using BG:D and make the stack attack the target like this:

This code might be usefull too: