Marguerite (stalker)

Chapter: 3 · Yard & Old House
Where: Old House 1F and 2F

Weak point

The head; while she patrols, every weapon does half damage

After you take the Stone Statuette in the basement and try to leave the Living Room, Marguerite slams the door and covers it in spiders. From then on she patrols with her lantern and, if she sees you, sends swarms of insects. She has 1500 HP, but while she roams every weapon does −50% and the Burner's burn does nothing (direct flame contact does: +150%). You can avoid her or stand your ground once for the achievement.

Reward

"Back Off, Mrs. B!" achievement if you drive her off: there is no other chance in the run.

1500 HP with −50% to everything while she patrols (datamined). On top of that the Grenade Launcher loses 40–50% with Flame Rounds and 75% with Neuro Rounds: don't spend grenades here.

Step by step

Clear the spider door with the knife (ZL + ZR to reach from further away): "Slash Slash, Slashity Slash!" achievement.
To avoid her: hide in the Old Shack, the save room next to the Gallery, until she leaves.
For "Back Off, Mrs. B!" (only chance): save when you reach the Old House and hurt her until she knocks Ethan down and leaves the house for good.
Shotgun or handgun to the head; the Burner for the swarms she sends.
"Less is More" achievement: one shotgun blast into a group of her insects kills two or more with one shot.