This achievement is obtained when you finish the game for the first time, regardless of the ending.
Given that this is an awesome little game, and with a not-so-little price, I recommend everyone to do a first playthrough to enjoy it, forgetting about guides, achievements, forced conditions playthroughs and such. Just play it, make your decisions and enjoy this fine game, with its great art style, voice acting and story.
But, if still there's someone that wants their 1000Gs in as few hours as possible, and given that there are five "ending" achievements and a "special condition playthrough" one, I want to throw here a little guide of how to get those 6 achievements in 3 playthroughs.
EDIT 20/01/16: As it seems, the "two playthough" guide isn't working for everyone, so I'm editing back to the "three playthrough" scheme, because some achievements exclude others in some instances:
- "I am the firestarter" excludes "Matchmaker" and "New beginnings".
- "Thicker than water" excludes "New beginnings".
- "Matchmaker" and "You'd just end hating each other" are complete opposites.
Playthrough 1: "Matchmaker" and "New beginnings" + Collectibles and miscellaneous.Be nice to everyone in this playthrough, and try to influence Nona so she and Ren end together. Slight spoilers follow.
*** Spoiler - click to reveal ***
- At the beach, when playing "Truth or Slap", don't say that Ren is lying.
- Short after that, when Ren and Jonas are going to jump the fence to get to the cave, don't follow them yet. Go talk to Nona and tell her nice things about Ren.
- When having to choose between helping Ren or Clarissa, choose Ren.
- This will lead you to Towhee Woods. When there, jump over the central chasm.
The It's A Me achievement in OXENFREE worth 21 pointsJump the crazy chasm in the woods.
- Never blame Jonas when you get blamed for what you did on the cave. Blame yourself if necessary.
- When tested by the ghosts in US Army RCS, try to give correct answers so Jonas isn't hurt. The answers are: US Army RCS, Cookies and 85.
- In Harden Tower, when Ren and Jonas fight, try to calm both, and when you have to choose a companion to go find Adler Estate keys, choose Jonas.
- At Adler's Estate, when searching the house, go talk to Nona and, again, talk about what a nice guy Ren is.
- When tested by the ghosts in Adler's Estate, try finding the three objects so your friends aren't hurt. The objects are: television (bottom left), painting (top left), portrait (top right).
- When you go to Bridge Stand to send a signal that opens the Bomb Shelter, the ghosts will make you a proposition about Clarissa. Don't accept it.
Don't use the tape recorders on the bridge to end the loop right away. Talk to Nona and tell her that Ren knew she liked him.
- Entering the bunker is a point of no return, so before doing it is a good moment to pick all the collectibles. Click on the achievements for their guides:
- Hug everyone before entering the bunker.
- IMPORTANT: When inside the bunker, help Jonas with the tape recorder or he'll hate you.
- When facing the ghosts underwater, don't leave through the back door. Save Clarissa using dialog options, or closing the gate with your radio.
- In the last scene, when Michael and Alex talk at home and he asks for your opinion, you'll have to tell him the following, depending on if he and Clarissa are still together.
· If they are still together, tell Michael "Go with her"
· If they broke up, tell Michael "Don't go to school".
If you follow these steps, during the "stat count" before the credits you'll unlock
Playthrough 2: "Thicker than water", "You'd just end up hating each other" and "I am the firestarter".Be mean to everyone in this playthrough, convince Michael to stay in town, and don't do anything to influence Nona so she and Ren end together. Slight spoilers follow.
*** Spoiler - click to reveal ***
- At the beach, when playing "Truth or Slap", when Clarissa asks Ren if he likes Nona and he denies it, say "He's lying", "He told me he likes her" and accept to slap him.
- Don't talk to Nona before entering the cave.
- When having to choose between helping Ren or Clarissa, choose Clarissa.
- In every occasion you get blamed for what you did on the cave, blame Jonas.
- When tested by the ghosts in US Army RCS, fail the answers (or don't answer at all) so Jonas is hurt.
- In Harden Tower, when Ren and Jonas fight, don't side with anyone, and when you have to choose a companion to go find Adler Estate keys, choose Nona .
- At Adler's Estate, when searching the house, don't talk to Nona.
- When tested by the ghosts in Adler's Estate, don't search for the objects so your friends are hurt.
- When you go to Bridge Stand to send a signal that opens the Bomb Shelter, the ghosts will make you a proposition about Clarissa. Accept it.
Use the tape recorders on the bridge to end the loop right away, without talking to Nona.
And as soon as the time loop ends, tell Jonas you accepted the ghosts' offer. Also, when you reach the radio inside the cabin, tell Ren and Nona what you did.
- IMPORTANT: When inside the bunker, don't help Jonas with the tape recorder. Go through the door instead.
- When facing the ghosts underwater, don't leave through the back door. Save Clarissa using dialog options, or closing the gate with your radio.
- In the last scene, when Michael and Alex talk at home and he asks for your opinion, you'll have to tell him the following, depending on if he and Clarissa are still together.
· If they are still together, tell Michael "Don't go"
· If they broke up, tell Michael "Go to school here".
If you follow these steps, during the "stat count" before the credits you'll unlock
Playthrough 3: "The silent, strong type"You can't use 
, 
or 
dialog options during this playthrough. Funnily enough, not talking at all will grant you some other achievements in case you didn't unlock them before (thanks Dugfreez for the confirmation). Spoilers ahead.
*** Spoiler - click to reveal ***
So, the main rule is NEVER use , or dialog options. If, for some reason, you get distracted and talk, dashboard, press menu and exit the game. The game only saves when you enter an area, and probably pausing and going to the main menu would be enough, but do it this way, just in case.
Also, keep in mind that there are some exceptions, so don't panic if your character talks sometimes.
- Some interactions with objects make Alex talk automatically, for example, opening some doors, using the radio transmitters or pushing the dumpster at the beginning. This is ok, the 
button talking won't void the achievement.
- You can interact with optional objects with , which will also trigger automatic dialogue (I did it a couple of times during my playthrough, and got the achievement anyways), but I recommend to go for this achievement once you have completed the game once or twice, that way you'll know what to do and will be able to just only interact using with the objects needed to progress.
- Also, DugFreez has confirmed in another solution that there's an unavoidable dialog option at the end, when you have to pick Alex's future: "The game shows a final still picture and you have 3 dialog choices using the X, Y, and B buttons. I tried to wait it out, but you can not. At this point you have to press X, Y or B. Thankfully the achievement still unlocks...so that last use of X, Y or B does not count against the achievement".
- I don't know if both possible endings (exiting through the gate / closing the tear) will grant you the other achievements. I went for closing the tear using the radio. Do that just in case.
If you followed these steps, during the "stat count" before the credits you'll unlock
And, if you didn't unlock them before