If you know the point you want the enemy to stay relative to, then some quick vector math can get you a relative vector pointing from one position to the other, and then you can use that to detect if the enemy is within the bounds.
Something like this should detect the distance the enemy is from a given point:
# we'll assume origin_point is a Vector2 containing the position
# we want the enemy to be relative to in this example.
# (also, you may need to swap origin_point and global_position below to get the right
# direction. I always forget the order...)
var relative_vector = origin_point - global_position
if (relative_vector.length() > 200):
print ("Enemy is more than 200 pixels away from the center!
# you can also get the direction to the center using the following code:
# var direction_to_origin = relative_vector.normalized()
# which you can use to move the enemy back into the circle.
else:
print ("Enemy is within 200 pixels from the center")
Hopefully that helps. From there, you just need to check if the enemy is within the circle, and whenever they are not, move them back into the circle and then resume idle movement. That is how I would handle having the enemies stay in a 200 pixel circle from a defined point.
