Ubistvo (courtyard, bus and tracks)

Chapter: A3 · Lanshiang: the Night Market, the Ubistvo, the Bus, the Train and the Stilt Houses
Where: 3-2 Shopping District: the zombie courtyard, the roof of a bus and the railway tracks

Weak point

The base of the chainsaw; the legs to make it kneel

In Ada's campaign its wild swing is instant death. Ada has no AI partner: solo it's hard, and with Agent in co-op his second gun helps a lot. Three rounds: getting the key back in the courtyard, surviving on the bus and two trains on the tracks.

Reward

You get the Back Street Key back. Possible medal: Used a B.O.W.'s attacks to kill all zombies in the area (let its swings kill the courtyard zombies; unconfirmed).

The first train's QTE buttons change with the difficulty. A single hit can be game over: don't reload within its reach.

Step by step

The chase: hold sprint, slide under the low obstacle and use the grapple at the end.
Before taking the Back Street Key: kill every zombie in the courtyard and ready Incendiary Grenades and a medium-range weapon. There are 5 crates, a Green Herb and a box with 2,000 SP.
Courtyard: crawling zombies keep dropping in and grab you: they're the real danger, so keep moving. Lead it to the edges of the courtyard. Sniper Rifle and pipe-bomb arrows, or the Assault Shotgun while backing off. Incendiaries on the zombies.
When it drops to its knees, run in and melee. 3 knockdowns + finisher and you get the key back.
Bus: survive until it's thrown off. When it charges, press action to grapple to the other end. Agent has no grapple: he has to slide between its swings on the opposite side. Slide under the green signs. Serpent Emblem #11 is at the first stop (scaffolding on the left): shoot it fast.
Tracks: there are 10 crates, but only grab them if you can spare a few seconds. It closes in whenever you reload: take a few shots and move.
1st train: a 3-button QTE. Then about 2 pipe-bomb arrows + a melee until the 2nd train: waggle the stick fast. That ends the direct fights.