Desperate Escape bosses

Chapter: DE · Desperate Escape: Out of the Tricell Facility
Where: Three acts in the Tricell facility: the dock (Transport Area 1 and 2), the turret area (Mounted Launchers and red gates) and the helipad rooftop (timed survival).

Weak point

By boss: Chainsaw Majini, leg shot then head; Gatling Gun Majini, grenade or magnum before he spins up; Executioner Majini, one magnum shot anywhere always stuns him; Reaper, grenade or Proximity Bomb, then the open chest.

Each area rolls its enemy set: the town set (Town Majini with Chainsaw Majini and Executioner Majini) or the base set (Base Majini with Gatling Gun Majini, Reapers and the red Executioner Majini, the Executioner's original concept with a flaming axe). The roll repeats in every area. Bosses here have less health than in the other modes: shotguns and machine guns do the job.

All of them except the Reaper swell and explode when they die: shoot them as they fall so the blast can't reach you. Every boss drops a large Score Star (1,000); this DLC has no treasures and no money.

Reward

One large Score Star (1,000) per boss, plus the Emergency Exit Key from the first dock boss. The bosses and the 2 fixed stars add up to 10,000–12,000 points on Normal: just enough for the S rank (10,000 or more).

Chainsaw Majini: red trousers (weaker, dies for good) or blue (stronger, falls and gets up berserk; those swings put you in DYING). Shoot a blue one as he stands up: he counts as dead once fully up. Fire or a Flash Grenade stuns a berserk one.
Gatling Gun Majini: he is invulnerable while firing; stun him with a grenade or magnum and finish with the tag-team combo.
Reaper: after a grenade or mine, when it turns back toward you, one shot into the open chest kills it (one source: a magnum to the chest core, in one shot).
Red Executioner Majini: one source says it only appears on Veteran or higher (unconfirmed).
Sources don't always split the helipad into two clean sets: treat this as the usual case, not a rule.

Step by step

Act 1, dock: the first boss bursts out of the big container to the north: 2 Chainsaw Majini or a yellow Gatling Gun Majini. It drops the Emergency Exit Key. On top of that container sits a fixed 1,000-point Score Star: shoot it.
Fall back toward the entrance and blow the oil drums to wipe out the crowd; against the Gatling, hide behind the truck. Lead a Chainsaw through the burning oil to stun him.
The second boss drops from the walkway above the truck (south): another Chainsaw Majini or a red Gatling Gun Majini (stronger).
Act 2, turrets: 2 bosses (Executioner Majini or Reaper) that don't appear on Amateur, and a third on the final slope behind the last gate. Any Executioner axe hit puts you in DYING: keep your distance, bait the overhead swing, get behind him and shotgun his back; when he kneels, go for the head.
Act 3, helipad: survive the timer (it starts at 5:00; at about 0:40 Doug radios and it jumps to about 2:40: roughly 7 minutes in all). Bosses come up the north-east elevator or leap down from the west tower: first a Gatling Gun Majini or a red Executioner Majini, then a Chainsaw Majini or a Reaper.
Lay Proximity Bombs a little in front of the elevator: they stun bosses. For a blue Chainsaw rising berserk, 2 Hand Grenades as he gets up.
Kill every boss fast: otherwise the last Agitator Majini (comes up with 26–30 s left, with 2 Big Man Majini) never shows. He turns into a Cephalo: keep a Flash Grenade.