I want to send a message from my enemy to the GUI script when it dies, how can I send a message from one script to another, even if theyre not child/parent of each other?
You would send the message to the component which then has to handle it and alter values accordingly.
The easiest way is just to use SendMessage and the other related functions on the target gameobject to call the function you want to be executed.
but alternatively you can also look for a specific component and call the method directly. this is just not as flexible