This achievement is for clearing Master Ninja mode.
Some general tips:
1. ALWAYS finish a Steel on Bone attack with the X button, no matter what the button prompt on screen says. If you mash X through a SoB, it will allow you to keep chaining and insta-kill any nearby enemy. A good strategy for large groups of enemies is to find a weak grunt, damage him until his clothes are covered in blood (XYXXXX works well), slide into him to knock him into the air, and hit Y to combo into a Steel on Bone attack. Hit X to finish it, and hit X again to chain the SoB to a nearby enemy.
2. The jumping bow attack is a safe and easy way to deal damage. This tactic is especially useful in the acid pit on Day 4.
3. Try to finish as many enemies as you can with an Obliteration Technique. It adds more energy to your ninpo meter.
These are the easiest, and safest ways to defeat each enemy:
Armored soldiers with glowing knives - on-landing 360YXXXY or XX>XY(hold)YXXXY. On-landing 360Y works with the Scythe as well.
Beret soldiers - X+A, A, Y with any weapon. Works every time.
Alchemists - Falcon Talons: Y, ->YXXXY. The forward+Y will only lift them when they're flat on the ground, so you'll have to wait a second after the first hit connects. Running + YYXXY can also instakill a healthy alchemist, but it only works when both Y attacks hit them while they're charging their magic. After you get the Blade of the Archfiend on Day 5, you can use running + XXX, >YXXXY for an instakill as well.
Invisible soldiers - Use shurikens to make them visible. After a shuriken *hits* one of them, they are vulnerable to the flying swallow for a second, so you can kill them instantly. On-landing 360Y with the Scythe and Dragon Sword are good as well.
Dogs - XYXXXX. If you hit the first five attacks, they will die before the final one, so you don't need to finish the combo.
Snakes - Scythe: XYXXXY and on-landing 360YXXY. With the sword, running + XX works well.
Apes - Scythe: XYXXXY and on-landing 360YXXY. With the sword, running + XX works well.
Scythe Fiend - Stay out of melee range, wait for him to do his jumping splash, dodge behind him, and use YYY. Retreat and repeat until dead.
Claw Ninjas - On-landing 360YXXXY with the sword or Scythe.
Dual-sword Ninjas - X+A, A, Y works, but they can block it. XYXXXY and on-landing 360YXXXY are more reliable.
Imps - X+A, A, Y with any weapon. Works every time.
For bosses, there isn't much to say about most of them besides learn their patterns and attack when they're open. But for the Regent of the Mask, use the Scythe. XYXXXY and on-landing 360Y destroy him. Fiend Ryu can be Izuna Dropped, so the Scythe and sword are good against him.
And finally, I've uploaded my first Master Ninja playthrough to youtube, so it can be used for reference if you're stuck on an encounter. The playlist can be found here: http://www.youtube.com/playlist?list=PL9906DCF435B70BFB&...