Total Achievements: (22)
100% completion time: 1-4 hours (Varies).
Difficulty modes:

• Easy
  
• Normal
  
• Hard

New Game+: No
Missables: Yes
Mode: Single-player

Achievement Types:
1) Story Related: (10)
2) Missable: (5)
3) Kill: (1)
4) Miscellaneous: (6)

We collect all 22 achievements in one playthrough, although not too hard we must focus where it is especially few missables. While we are progressing it is very important we carry the gnome that is found in chapter 1 all the way to the end before the game ends for one specific achievement so you know the drill from older Half-Life related games. Lastly, we need to be wary of sightings. There are no achievements related with Difficulty so play whatever you want.

1) New Beginning, Waste Disposal, Pest Control
2) Sightings: 2/3
2) Achievements: 10/22
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Freeman
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Achievement #1: Miscellaneous. Beginning after teleportation is a crowbar stuck to the wall in front, proceed to it and you get the achievement.

This one is still at the very early level, you can find the Gnome on the wooden table where the Resistance members are.

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Shock Result
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Achievement #2: Miscellaneous. Entering the next floor is the barrier along with the plug on it, disconnect it by pulling while getting hurt and you get this achievement.

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New Beginning
Complete Chapter 1
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Achievement #3: Story Related. Interacting the Valve while it turns automatically will open the door and give us an achievement.


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Unforseen #1
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Achievement #4: Missable. Our first G-Man sighting can be found where the outside is after dealing the barnacle, just look through with zoom (Z key) and you will see a few seconds of him moving.

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Burn!
Who knew gas could be so hot?
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Achievement #5: Kill. This one can be triggered easily, by the next room are pipes and there is gas coming out, let the zombie walk towards you and he will burned, from there is an achievement.


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Waste Disposal
Complete Chapter 2
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Achievement #6: Story Related. After dealing with all waves of zombies, he will get out and you can follow him to the metal door to unlock this achievement.


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Unforseen #2
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Achievement #7: Missable. Reach to the Resistance compound. Immediately after the Resistance guy pull the lever, save and go to the right gate where the mountainside is, zoom to the APC of the bridge which the G-Man makes his appearance in there, unlocking you the achievement.

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Quick Maths
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Achievement #8: Miscellaneous. This one is from the room where you need to open the door on the screen monitor, this is straightforward so after all lights are on and door opens from pressing buttons you will get this achievement.

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Collateral Damage
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Achievement #9: Story Related. When you take the elevator, there is a gunship boss but luckily it is dealt with thanks to the RPG at the boxes where the AR2s are, destroy the gunship and you unlock the achievement.

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Pest Control
Complete Chapter 3
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Achievement #10: Story Related. Walking inside the tunnel after the APC and that sniper will unlock this achievement.

1) Crack In Defense, Black Coast, Final Push, The Beacon
2) Sightings: 3/3
3) Achievements: 22/22
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Shut up!
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Achievement #11: Miscellaneous. This is located inside the room with a radio with the Magnum you can get first time after the Lambda locator sign, destroy the radio with any weapons and you unlock the achievement.

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Crack in Defence
Complete Chapter 4
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Achievement #12: Story Related. While either using the muscle car or walking through the tunnels with zombies, you will unlock this achievement before the loading screen.

I prefer not to take the muscle car with me because of the gnome.


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What was that?
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Achievement #13: Missable. This is your last sighting, while walking with the gnome you will see a brief second of the dark figure coming out at the top of the lighthouse, unlocking the achievement.


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Whee!
Go down the slide
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Achievement #14: Miscellaneous. Before you enter inside the lighthouse while trying to disable the combine shield barrier, you go left to where the ship wrecked and a house. Behind it is a playground with a box where you then can walk to the slide to the top to unlock the achievement.


Before proceeding inside the abandoned house, we first must find a car battery inside the house and grab the key inside the small building outside so we can use it for the other achievement.

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Flushin'
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Achievement #15: Miscellaneous. Going up the stairs while zombies roam around the abandoned house is another car battery inside the bathroom and a toilet, just interact with it.

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Going The Extra Mile
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Achievement #16: Missable. Located in the second floor, you will need the key to unlock the armoury.

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Black Coast
Complete Chapter 5
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Achievement #17: Story Related. Before the loading screen, this unlocks after the abandoned house while inside another building to the next level.


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Survivor
Survive the Battle at the beacon's bridge
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Achievement #18: Story Related. A battle will ensue here with multiple Combine soldiers and elites as well as few Striders, you got explosive barrels and lots of RPG rockets as well as other stocks. SAVE as many times as you want. After at some point where a lot of Elites and Soldiers come out with the headcrab zombie capsules you can move to the opened door to your left and down the stairs

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Final Push
Complete Chapter 6
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Achievement #19: Story Related. Before the loading screen while crouching to the next level you can unlock this achievement after dropping down and fighting against the Combine Soldiers.


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Get Gnomed!
I'm a G'nome! Bring your gnome to the beacon's core
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Achievement #20: Missable. When entering the final level and destroying the core, the window will break but save doing this and you can launch the gnome with your gravity gun to it luckily this is nothing complicated to do.

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The Purpose
Fullfill Your Purpose
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Achievement #21: Story Related. By the time you already destroyed the core you get this achievement.

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The Beacon
Complete Chapter 7
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Achievement #22: Story Related. After listening to G-Man and before credits you unlock this final achievement.

As a Half-Life fan I really love more of mods to play relating to Half-Life or 2 so this should come as to no surprise. Although flawed but simple even with achievements this mod does nothing to be masterpiece but it is a filler to the content anyways so it's okay.



100% finished, keep it up people and good luck :)

If you want to consider donating, I have the link here so you can send your money. Otherwise if not then that is fine, continue using this guide at your own benefit I won't ask too much.
https://www.buymeacoffee.com/Diviision