First of all, I want to say much respect and thanks to xTMDxMorbidDead for taking the time to record this entire game for help for this achievement. I just want to make a supplementary solution with some tips I feel he missed out on mentioning.
* Buy the Feather, Anchor and Magnet as soon as you can. These can help you get some lucky "perfections" on your first run of a level if you stay careful. Always nice not to have to replay a level. Even if you read this solution after finishing the game, make sure you buy these.
* Buy the XXYY (Morph Tornado) and XYYY (Morph Tendrils) combo attacks after buying the attachments. These are Scarygirl's best attacks and they can be incredibly powerful against groups of enemies.
* You will also want to buy the Grapple+B attack (Anaconda Squeeze), which lets you steal life from an enemy. Use this whenever you've been hurt at all, even just one quarter of a heart, and you find a lone enemy or two. Just use light attacks until they're grapplable and then grab the free life.
* Play through the story and collect hearts before you even begin contemplating this achievement. In this game, anything an enemy does to you takes precedence over anything you do to an them. Meaning if you're in the middle of a combo and beating the shit out of them, they can still get a dirty potshot in and stop your combo. This is especially true for the notorious blue guys. They simply WILL get hits in on you no matter what you do, it's just not possible to take out a bunch of those guys without getting hit. So you'll need a big stock of health in order to pull this off.
* The blue guys. What you want is the spinning tentacle attack (XXYY). It will fly through a group of blue guys and kill them all in one fell swoop, making that bitch of an airship level much less frustrating - the width of the attack stretches across almost the entire ship. This is the only time I'll say something negative about xTMDxMorbidDead's videos: he's way off base about the "just mash Y" tip for the blue guys. It doesn't work at all. Use XXYY. A less useful tip is that you can also stand back and let them take their dirty pokes at you, and just counter them with your shield.
* Other tips for the airship: Take it as slow as you can. If there's nothing but lumberjacks, keep abusing your shield to bounce back axes, bombs and lunges and then just cheese your way through them with X attacks, one at a time. Don't go crazy with combos unless you know you can pull them off without getting hit. In the second half, you can change to abusing XXYY to clear out the entire airship in one swoop. This level is so unfair that even with that powerful attack, it's going to take a few tries, but XXYY should take some of that insanely frustrating edge off. Also, don't forget about Grapple+B!
* Perhaps most importantly: take breaks! Play something else. Walk the dog. Do a few levels at a time. This is going to be frustrating, and if you attempt to knock this game out in just a few sessions, you're liable to lose your mind. This game is a lot of fun on the first playthrough, but when you're trying to do it without dying, it becomes apparent just how horridly unfair and meanspirited this game is..