Uroboros

Chapter: 1-2 · Urban District and Furnace Facility
Where: Furnace Facility: it appears in the main passage and the fight happens in the square furnace room, which has a control panel and 2 gas cylinders.

Weak point

An orange core that sometimes shows on its arm-like part. The furnace kills it in one go on Amateur and Normal. The gas cylinders, once it has absorbed them.

A Kijuju man the masked Jill injected with Uroboros: he rejected it and became a mass of tentacles. It appears when you take the Furnace Key from the corpse by the furnace controls and head back to the locked door.

There are two ways: the furnace trap (fast and free, but it melts the Gold Ring) or gunfire (slower, but it drops the ring). Use the furnace on a first run and come back for the ring on a replay with strong weapons. Its hits attach leeches that drain your health for a while.

Reward

Gold Ring (₦5,000), only if you kill it without the furnace. "Uroboros" figurine: 10 BSAA Emblems and Chapter 5 cleared.

Amateur and Normal: one trap kills it even if you haven't damaged it.
Veteran: it may survive one trap if lightly damaged.
Professional: it may survive two.

IGN: it "can literally be over in seconds". On Professional the handgun-ammo briefcase after the fight is missing.

Step by step

Before the fight, knock over the 2 gas cylinders in the furnace room (you can do it before taking the key).
Don't shoot. Fall back down the narrow corridor into the furnace room: a shutter seals behind it when it enters.
If it passes a knocked-over cylinder, it absorbs it. Shoot the cylinder once it is inside, not while it is only nearby.
Furnace: lure it into the furnace chamber, step out and hit the control panel at once (or tell AI Sheva to). A few shotgun blasts keep it inside while the door closes.
Gunfire (replays): Gatling Gun, Rocket Launcher or S&W M500, plus the cylinders and Hand Grenades. This way it drops the Gold Ring.
Afterwards, use the Furnace Key on the locked door: no enemies are left until the end of the chapter.