Moonscars

This achievement is for killing the penultimate boss Red Irma, The Parent Flesh.

You'll find Red Irma at the top of The Apex, think of the Apex as 3 towers, the left tower allows you pick up items and progress through the area, the right tower is where the Moon Chapel is (see Cruel Queen questline) and the central one is where you'll find this boss. There is a tutorial node that warns you about passing a point of no return, flick the switch and take the lift up. If you're going for the Cruel Queen quest then you'll want to make sure Yarema is where he's supposed to be at the top of the Moon Chapel before you proceed. In my opinion this boss was pretty easy and I had her beat on my second attempt with no Spite bonuses. I'm sure you can use pretty much any loadout you're comfortable with but I will list what I used.

Loadout recommendations:
Amulet Stones (not that important tbh, I used..):
1) Fierce Fencer Gemstone (Damage bonus)
2) Dashing Gemstone (Double dash)
3) Slashing Dash / Projectile Protection / Deep Wounds / Witchery Cost / Ichor Regeneration (if you have it)

Special Attack:
Whirlwind

Witcheries:
1) Corrosive Touch
2) N/A - Chain Boulder could be good, free choice otherwise.

This fight starts as a straight Doppelganger fight and is pretty easy if you just fire up Corrosive Touch and hit your special attack with and dash away afterwards, rinse repeat. You will be getting Hex and Poison damage and you will melt Red Irma's health bar. She's quite slow moving and really quite passive compared to some of the later Doppelgangers you will have beaten. She can use an overshield making her immune, just keep spamming your Whirlwind and dashing away, the Hex damage tick willl stagger her at the very least. There will be the odd red tracking orb or non-tracking spear projectile fired at you from the moon. Do your best to dash out of the way of these. As you will be dashing back and forth pretty frequently you'll probably avoid these most of the time anyway.

NOTE I: The red tracking orb will heal the Doppelganger if it hits her. I wouldn't worry too much about it though.

NOTE II: As first phase ends you will go through some dialogue and regain control whilst the screen fades out. Heal up if needed and hit her with a Whirlwind to refill your Ichor before she disappears. Head to the middle or to the left, and start jumping even if you can't see anything as the arena environment is still active and you will start phase 2 already on one of the platforms described below, allowing you to hop up and grab some easy swings at Red Irma.

Here's a gameclip from my final 60 seconds in the first phase:
Phase 2 sees Red Irma suspended in the air and some platforms appear in the arena. They look like the temporary platforms that disappear after half a second but they aren't. She will fire one of 3 projectile attacks and 1 AOE attack and you will want to focus on avoiding them entirely before going for any hits.

Her attacks are as follows, and as far as I know they're randomly selected:
1) Surrounds herself with 6 tracking orbs, shoots them at you 2 at a time.
Standing directly beneath her is beneficial as dodging them will likely mean she whiffs them in to the ground. If you head to the sides they've a better chance of surviving if they miss and hitting you on the second attempt.

2) Shoots non-tracking spears at you.
Stay mobile, you shouldn't need to dash to avoid these unless you are directly beneath her or she is low to the ground.

3) Rotating Laser beams in a cross shape.
This criss cross laser spins fairly erratically, but as long as you're paying attention and dashing you should be OK. I recommend trying to stay in a corner on the ground so you are at the widest possible distance between any two of the lasers giving you the maximum dashing window possible. When this attack starts, if you are right next to her she won't actually be able to hit you with these until she starts moving so you can get in some cheap hits this way before dashing away

4) Pulse AOE.
A circle of cloud will appear around Red Irma, you've got a second to get in a free hit or two, then double dash away to avoid the impending circular explosion.

As each of these attacks ends (and none of them last that long) you should be prepared to jump up to the nearest platform to her and get in some damage, I used light attacks but you could probably get away with Special attacks too. If you have Ichor spare, then make use of Corrosive Touch as you jump up to bag some free poison damage.

She may also spawn an enemy on the ground level (she did this twice during my successful run). The screen will fade out on spawn and death of this enemy. On death you should try to position yourself in the middle or left side again and start jumping up so that you can mantle on to the platforms which will reappear before the screen becomes fully visible again so you can get back to Red Irma quickly for extra damage. I dispatched this enemy using the same strategy that I did for the first phase. Spamming Special attacks and dashing away, repeat, repeat, repeat. Chain Boulder could be a good shout here if you have the Ichor to spare. Your Special attack will regen Ichor extremely efficiently so you might as well use it up - or you can just play safe and save it for healing. Whichever you prefer.

Before long, you should be done.

Here's a gameclip from my final 60 seconds in the second phase:
If you're going for:
Then make sure to speak to Ion and exhaust his dialogue, then once you've spoken to everyone else go speak to him again back at the newly accessible part of the Mould Workshop before the final boss arena.

If you're going for:
Then head back to the Moon Chapel and speak with Yarema and Yadwiga, exhausting their dialogue.