Godot Hot Code
This is intended as a cheat sheet for Godot, but I haven't kept working on Godot, so it's super basic right now.
Get Screen Size
Tags: gdscript
OS.get_screen_size() # The full computer screen size
OS.get_window_size() # Just gets the game window
get_viewport().size # .x / .y for width/height. Just the game window
Get Mouse Position
Tags: gdscript
var pos = get_viewport().mouse_position()