The best part is that if you’re already a Nintendo Switch Online subscriber, the free 12 months of access will actually be added to your existing subscription.
To claim your prime loot, go to the Twitch website, sign in to your Twitch account (or click Try Prime for a free trial) and it’ll redirect you to Nintendo’s website where you have to sign in with the account linked to your Nintendo Switch. Once you’re in, it’ll bring up the Nintendo Switch Online Membership Status, so just click Next and then hit Redeem.
Remember that all Amazon Prime members have Twitch Prime, so if you're already a Prime member, you're good to go.
The catch is, of course, you only get 3 months for free to start out with. If you want the other 9 months, you’ll have to stay a Prime member for the next 60 days after you’ve claimed the first one. So if you decide to go with a free trial, you’re out of luck.
According to the website, you’ll be able to claim the first 3 months until September 24, 2019, while the 9-month subscription expires January 22, 2020. So there's plenty of time to claim the offer.
One of our favorite features of Nintendo Switch Online is the ability to cloud save, simply because there's no other way to back up your data, so we highly recommend you grab this deal while you can. The service also allows you to play titles like Super Smash Bros. Ultimate and Splatoon 2 online, and gets you access to a growing library of classic NES games.