I think signals aren't the best way to do what you want to do.
A better way of implementing that is instead of using signals , make a variable named whatever node you need to modify ("some_node") and export is as
NODEPATH, something like this :
export(NODEPATH) var varname, so that you can just select whatever node you want from the mobs node inspector.
Then, once you do that, you check if its colliding with the player, then do the modifications or call a function to the node you set in the mobs inspector. make sure to use
I hope this helps you!