Mergo's Wet Nurse
When you finally reach the peak of Mergo's Loft, you'll find the titular baby Mergo in her crib. Or do you? Mergo's Wet Nurse will drop in, ready for battle.
The Nurse looks very intimidating with her myriad of blades, but the best place for you to be is up close. This way, you can slide around her while she slashes, opening up her back to your own attacks. She may slice in a whirlwind motion, in a three-slash combo, or in a half circle in front of her. In all of these cases, sidestep behind her and use the opportunity to deal damage. She may also unleash a fury of slashes will marching forward. This will chip away the majority of your health if it connects, so you may want to just back up for a moment.
The only other trick up the Nurse's sleeve is a purple fog that envelopes the entire arena. When this happens, a clone of hers will randomly appear and unleash one of her attacks. This fog goes away after some time, so you may just want to avoid all conflict until it subsides. Otherwise, look for brief opportunities to get a few hits in - just don't let yourself get between the Nurse and her clone.