Hey dice, this idea can be realised much easier, you do not need to create an entity and let the player walk there! Just use MrGuests method to trace from your mouse position to the ground and when you hit your terrain/block you have the vector your player will have to walk to.

@MrGuest don't you need to do a vec_to_screen on the mouse position at the beginning? And you have to trace down to -5000 not to 5000 otherwise you'll trace up into the sky.