One thing that I consider a pet peeve is a video of a trophy with the title (something something guide) and just someone showing that they are cracked at the game. It's good for them, but who is it for? At least don't write as if you're trying to help people who want the trophy. Sorry for the rant, but I found 8 videos from different people flying through enemies with the title "Guide" specifically for this one. Anyway, there is an easy way to get the "You reached the right number" trophy, which requires a multiplier of 15. Go to the chapter "Curtain Call" and head to the secret challenge "Slasher." The challenge is by far the easiest way to get as it doesn't require any skill; just start the challenge, jump to the left, destroy the machine, and then head right through the disappearing bridge on the right. Throw a shuriken and, climb the drone, jump to the one in front of you to destroy a group in one blow; that alone will give you a multiplier of 12; throw another shuriken to the bot in the middle and make him fall to one of the other groups.  With that route, it's impossible not to get it. I hope it was helpful. Happy trophy hunting!