You're coding in C++. Forget about global variables, try and make a class that has all those variables. If you can't fit it in a class or function you're quite possibly doing something wrong. Globals are considered dangerous when you tend to use them as much as you do. It also cleans up your code a lot, 2000 lines is a lot, especially when I think you could make it a lot more readable by splitting all the code up in classes. Having the functions that need the member variables of a class in that same class or friends of that class also eliminates the need to pass every variable and allows you to simply make private "safe" data members.
2, 3, 4 should be solved by learning and using classes. 1 is very advanced and will make your eyes bleed and your program deadlock. ;-) Assigning each monster its own thread would do you little good since you'd have to lock every variable/array it'll access and unlock it... It will probably slow down the program quite a lot.
Well, really try to encapsulate most of the functions and variables into classes. That should be your focus. I like the idea and your work on the RPG though! Very cool. :D
The monster hit algorithm could be something like this right:?
For each monster
for each hit coordinate
check if the monster.location == hitcoordinate[n]
if so do damagerollorsomething
