The drop rate is extremely low. I was lucky to have mine drop on the 8th or so Griffey, because I've heard reports of it taking 20+ kills.
Oh damn that sucks. I got lucky then, I ended up getting the drop around 2x Griffy's. and one dropped a leaf so GG xD
This is the only guide I found to obtain ninja storm. Could anyone advise if the bug from boogie is fixed? It has been 5 years.