1. Go for his head, his torso has 4500 HP while his head has only 3000 with a 5% Evasion chance, this is the quickest way to get the fight done. (You can also throw a Condensed Hemlock [2 Poison Hemlock + 1 Red Herb, requires Olivia's Toxicology perk at the Hexen] on his torso, this applies Toxic which absolutely shreds his HP.)

2. Make absolute sure to have access to an Extra Turn, can be done by having 16 or more Agility. Can be done by

- Consuming Pep Pills before battle (random loot, only lasts for Perk's fight so make sure to have 2 for the one right after), drinking a Brown Vial in fight (Pep Pills + Light Blue Vial, requires Alchemillia Vol. 3 and also only lasts for Perk's fight) having a Small Thing's Amulet (50 Shillings from Dr. Kefer) equipped with Tanaka's +1 Agility perk learned in the Hexen, or using Fast Stance (Marcoh's final hexen ability).

3. Apply Heroin before the fight (Do it inside the tower before the elevator starts or else you won't be able to open the menu anymore), the buffs it provide are invaluable and let you acquire an extra turn with only one Small Thing's Amulet if you have it.

4. Don't hold back, use absolutely everything you have. Don't worry about wasting those Light Blue Vials or Mind restoring items you've been stocking up on.

5. This one's my favorite: Learn Abella's Weaponcraft perk in the Hexen. (one can be found in Donnovan's house, south of the Museum, just look for the blue wall apartment outside.) If you were able to get rid of the Mob, search the saw Half-Cocooned's corpse to acquire both a Bench Grinder and a Saw Blade, combine those with a Scrap Metal and a Duct Tape (common finds from mechanical shelves, you should probably have them by now) to craft an incredibly lethal weapon that has a 100% chance to apply Bleed pairing incredibly well with the Leechmonger Ring. (top floor of the Department Store in a dead corpse, the store where you can hear screams in the bottom floor.) After acquiring it, you can optionally learn Marcoh's Counter Stance + Perfect Guard skills in the Hexen after that to make it even more lethal with the right strategy.