This is pretty easy to get off on just one enemy in the 1st level. 1st thing you need to do is get the POW upgrade which can be found in a crate in the level. When you have that, your character will always hold a couple blades in a cross formation whenever he walks. Find a ninja preferably one by himself. Walk towards him while he throws a projectile at you. Your character will simply deflect it automatically. If you walk close enough the ninja will jump over you and and throw another. Just turn around and walk towards him again and deflect another. Just keep repeating that back and forth until you've deflected 10 projectiles.