Entropy : Zero is a modification for Half-Life 2 created by Breadman and released on Steam on October 10th, 2017.
It follows the exploits of a wise-cracking, sociopathic Civil Protection officer only known as "Bad Cop". Eleven months prior to the events of Half-Life 2 proper, Bad Cop finds himself stranded in snow-covered City 10 after a train crash leaves him the Sole Survivor of his squad. An outbreak of the "CFLU" some time prior to his arrival had forced the Combine to abandon the city, allowing the Resistance to swoop in and take hold of it for themselves. With his circumstances leaving him the only one who can set things right, Bad Cop sets out to clear the streets and subways of infestation, Resistance or otherwise, and reclaim the city for the Universal Union.
A sequel, Entropy : Zero 2, was released on August 20th, 2022 and follows Bad Cop's story in the time between Half-Life 2 and Half-Life 2: Episode One. A spin-off by a different team of modders, titled Entropy : Zero - Uprising, was released in April of 2023, showing a Civil Protection officer's perspective of the City 17 Uprising.
Entropy : Zero contains examples of:
- Achievement Mockery: The achievement "Bullet Hangover", awarded for dying one hundred times.
- Action Prologue: The prologue drops you right into a Civil Protection raid on a Resistance hideout.
- All There in the Manual: There's an extensive amount of lore write-up (compiled here
for easy reading) which explains story elements that are only implied in-game, such as why CFLU is more dangerous to Combine personnel than to regular humans, the measures the Combine took to try and maintain power in City 10, the civilian exile to City 17, and the purpose the Quantinode core in Pillar 10 serves. - Blackout Basement: The third chapter, "Low", centers around Bad Cop’s journey through the subways and tunnels beneath City 10, which are almost entirely devoid of lighting.
- Call-Forward: On a whiteboard in one of the Resistance’s strongholds, Laszlo is credited as the one who created the overrides for the Combine turrets which reprogram them to be friendly to citizens, as an explanation to why he’s referred to as "the finest mind of his generation" by a friend of his in Half-Life 2.
- Cavalry Betrayal: Inverted. A Metrocop that Bad Cop rescues from a Resistance stronghold takes the opportunity to knock him out while he has his back turned, revealing himself to be none other than Barney Calhoun.
- Elite Mooks: The Vortigaunts in the final chapter can take way more punishment than all the enemies before them, and they hit extremely hard too.
- Escort Mission: After a power surge disables his helmet's night vision, Bad Cop is forced to escort a flashlight-bearing Stalker through the tunnel system ahead, which is infested with zombies and headcrabs, so that it can open the way to a Combine transit hub on the far side.
- Hoist by His Own Petard: A citizen locked in a room in the City 10 underground throws a grenade at Bad Cop through a high-up opening in the wall. You can throw it back if you're quick enough and hear a panicked reaction from the citizen just before he blows up.
- Idiosyncratic Difficulty Levels: "Good Cop", "Not So Bad Cop", and "Bad Cop" take the place of Easy, Normal, and Hard.
- Nice Job Breaking It, Hero: Bad Cop's train derailing is revealed through Story Breadcrumbs to have been intentionally caused by the City 10 Resistance, whose leader ordered the derailing as part of a deal with the G-Man. Little did they know how screwed the whole city would be as a result.
- Optional Stealth: You have the option of sneaking through one of the Resistance's strongholds by taking a specific path through it. Given that they have reconfigured Combine turrets set up everywhere to shoot intruders as soon as the alarm is raised, it's the more preferable course of action.
- The Plague: CFLU, a contagion which is dangerous to humans and Combine personnel alike, and which forced the Combine to evacuate City 10.
- Protagonist Title: The fourth and final chapter, "Bad Cop".
- Shout-Out: Some of the achievement names reference Valve works, including "More Gun", "Still Alive" and "Baby Sittin' Job".
- Super Prototype: In place of the standard AR2 from Half-Life 2 is a prototype AR2, which boasts a higher magazine capacity and more stopping power but also has much more intense recoil than its mass-produced counterpart.
- Take That!: One of the graffiti messages in the mod claims that "Cold silence has the tendency to atrophy any sense of compassion". It’s found right below a Lambda graffiti with a "3" right next to it, confirming it to be a dig against Valve for their lack of communication regarding the long-awaited Half-Life 3.
- Title Drop: The large overhead screens indicating Pillar 10's core status initially read "Entropy: Optimal". During the final boss fight, this status changes to "Entropy: Dropping" and eventually "Entropy: Zero".
- Turned Against Their Masters: A smaller-scale example involving the Combine floor turrets, which the Resistance have reprogrammed to be friendly to them and hostile to the Combine. After Bad Cop reconnects the turrets to the Combine network, they become Combine-affiliated once again and start gunning down rebels all across the city.
- Villain Protagonist: As a Civil Protection officer, Bad Cop is an enemy of the Resistance who have set up shop in City 10.
