**Edit - The 'mystery game' which is avaliable to download for FREE today (providing you've been grabbing the games every day) is the really fun Space Pioneer which I reviewed HERE. Space Pioneer only came out a few weeks ago and offers hours upon hours of entertainment with it's F2P to Switch conversion, removing all microtransactions and premium currency.**
To celebrate their 15th anniversary, Qubic Games are giving away ten of their Nintendo Switch titles over the course of ten days (technically 14 days). Unlike other publishers who may run a competition or some sort of giveaway on Social Media, these ten games are free to every single person who owns at least one game from the Qubic Games catalogue (NA, EU and AUS regions only).
The way the giveaway works is:
• From today (the 10th December) until the 15th December, ROBONAUTS will be 'free' to everyone who owns a game from the list below.
• Every day from the 16th until the 24th of December a new game will become free to 'purchase'.
• In order to keep the chain rolling, you MUST 'purchase' the free game each day as having that game in your library (and all previous 'free' games) is what triggers the next game to be free.
• All the games, with the exception of ROBONAUTS, are only 'free' for 24 hours - if you miss your chance then it will break the chain.
• If you do break the chain and miss a game, it'll be on sale once the next freebie goes live, offering you a discount should you wish to activate the promotion again.
So, if you forget to redeem the game on the 19th, you'll have to buy the game you missed in order to reactivate the free promotion on the 20th. In a way, it reminds me of a mobile game which has daily bonuses, requiring you to 'check in' every day to keep the benefits rolling.
You must own at least one of these games:
Akane (£4.49 89p)
Akuto: Showdown (£6.99)
Barbarous: Tavern of Emyr (£6.99)
Blazing Beaks (£13.49 £2.69)
BRAWL (£8.99 89p)
Castle of no Escape 2 (£6.99)
CHOP (£8.99 £4.49)
Coffee Crisis (£8.99 £1.79)
Coloring Book (FREE)
Escape Doodland (£8.99)
Geki Yaba Runner Anniversary Edition (£2.69)
Get Me Outta Here (£4.49 £2.24)
Grid Mania (£1.39)
Jumping Joe & Friends (£1.79)
Koloro (£8.99)
Laser Kitty Pow Pow (£2.69)
Mana Spark (£8.99 89p)
Mini Trains (£5.39 89p)
Monster Bugs Eat People (£1.79 89p)
Not Not - A Brain Buster (£1.79 89p)
Odium to the Core (£4.49)
One Strike (£4.49)
Party Treats (£1.79)
Puzzle Book (£3.59)
#RaceDieRun (£8.99)
REKT! High Octane Stunts (£5.39)
Rimelands: Hammer of Thor (£8.99 £4.49)
Robonauts (£3.49)
Shipped | UK (£5.39 £2.69)
Soul Searching (£8.99 £4.49)
Space Pioneer (£8.99)
Super Hero Fight Club: Reloaded (£8.99)
Unit 4 (£13.49 £1.34)
UTOPIA 9 - A Volatile Vacation (£8.99 89p)
Warlocks 2: God Slayers (£15.99 £1.59)
Wondershot (8.99)
Wreckin' Ball Adventure (£4.49)
All of the above prices, including the discounts, are most likely to change over the course of the promotion - this is what they were like as of today (10th December 2019). Also, the North American e-shop has it's own discounts and promotions, so games which are discounted over on the EU store may not be discounted on the NA one and vice versa.
As an additional note, gamers who use the EU (including UK) or Australian store wont be eligible for the promotion if the only Qubic Games game they have is either Space Pioneer, Get me Outta Here or Monster Bugs Eats People, those three games are valid on the American store but not ours.
If you do only own these, or you wish to participate in the giveaway without making a purchase (although I do encourage you to support the publisher), you can pick up the Coloring Book game for FREE and that will trigger the ten days of free games - we just tested and this seems to work.
What are the free games?
In total there are ten games spread over fourteen days. Why fourteen? The first game, Robonauts, went free today and will remain free for five days to allow people time to jump in and grab the first game in the chain of freebies. Then, once the clock rolls over to the 16th December, you'll get a new game every day until Christmas Eve. Here are the games you'll be able to grab for free!

The final game, on the 24th December, is a mystery at the moment but the FAQs on the webstie does state it's one of the 'more premium games' they've released this year.
For more information on the giveaway, check out the official website here: https://qubicgames.com/15years/