4. Ng5 is one of the main lines against the 2 N's Defense. But anyone who has done even a little study of the opening will know not to play 5 ... Nxd5. Hoping your opponent falls for that is not the only reason to play 4 Ng5.
When I first played chess, I was hoping people fell for 5.Nxf7 with a fork. I was a 700 on chesskid then.
Funny how many players go for sideline or tricky openings and become disillusioned with it. Like it or not, it pays to gird up and spend the time and energy playing and studying a major, solid opening. But seems the hunt is on for the golden opening that will bring. with little effort, sought after victories.