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As of November 9th 2020, all event skins are craftable using scrap!If the achievement doesn't unlock, quit the game and boot it back up. Several users have experienced this.
I'll leave all the old information up just for the sake of people knowing how it was obtained originally.
FINAL UPDATE!: There will be no more events. The skins will be craftable in January 2020.
As of February 15th the update to make them craftable is still pending from The Coalition. The below quote is from TC Octus on Reddit.
We've postponed the Gears 4 sunsetting stuff until Summer so the team can keep focusing on improving 5 above all else. We're locking down plans now to communicate well ahead of time what we plan to do, but it won't be for quite a while.
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The Coalition started Versus events for Flaming Weapon skins back in August of 2017.
WARNING!!!: DO NOT SCRAP THE SKIN REWARDS UNTIL YOU UNLOCK YOUR ACHIEVEMENT. YOU NEED 5 AT ONE TIME.Above information credit to
AceMcCloud. Thanks for confirming!
5/3/18 EDIT: The event reward distribution has been updated. They are now tied to Xbox Challenges with zero Gamerscore. There is tracking progress with the challenges, so no need to manually track yourself anymore. Once you have unlocked the appropriate challenge, go to the MOTD (Message of the Day) on the Gears 4 menu, and click 'Claim Reward'. It will redirect you to the Gears official website where you will log in with your Xbox account. Click 'Claim Reward' on the website page and you should receive your reward instantly. Coalition has stated to allow up to 48 hours for the reward to appear.
Alternatively, after you've unlocked the challenges, you can go to the new 'My Reward' page on the Gears website, login, and claim the reward.
https://gearsofwar.com/en-us/my-rewardsDuring these timed events you need to register through the main menu on Gears 4 that will redirect you to GearsofWar.com. You'll then hit register on-site. Each event will have criteria that must be met to be eligible for the Flaming skins. You'll need to manually track progress during these events as there is no in-game tracker.I will post any upcoming events as they are announced and edit this solution and make a comment to it as well.
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12/10/17 EDIT: I created a leaderboard for both of the weapon skin achievements in Gears 4. I will send a mass PM to all users that have joined the leaderboard each time a new event is announced. I will also stick to my word and make edits to the solution and post comment updates in addition to the leaderboard PMs.
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12/21/17 EDIT: Distribution of past several event's weapons skins added in. Also updated formatting of solution. Let me know if this looks more appealing and cleaner for you guys.
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List of events
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Event 13 - Feb. 22nd - Mar. 8th: OSOK Classic / OSOK Horde-
https://gearsofwar.com/en-us/community/whatsup-feb21-2019-- Tied to 2 challenges during the event that both reward 5 random Flaming Skins
-- Duplicates do not count for extra progress
-- You may have to close and relaunch the game in order to see achievement progress update
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If you have any further questions, feel free to comment. I will answer as soon as I am able to.
~Slayer