Aha got it!
Heres my solution:
First do PointX2-PointX1 and save it in a variable. Then do PointY2-PointY1. This gives you a triangle (This is used for calculating slope too.). Now do ToDeg(atan(Variable(X)/Variable(Y))). Save that to a variable and you got the angle between 2 points! Note that in Game Develop, angles are reversed vertically : so 90 degrees for this equation would be 270 degrees, but 180 degrees would still be 180 degrees.