Switch Online costs $19.99 in the US, but now, you can get it for free. The process is a little convoluted, however. Twitch Prime subscribers can initially claim a free three-month membership, then, after 60 days, they can get another other nine months. We're assuming this will stop people for signing up for Prime for just a month to get the free year of Switch Online.
The deal is available to both new and existing Switch Online subscribers. Keep in mind Twitch Prime is part of an Amazon Prime, which is $199 a year (or $12.99 a month). So don't go out and get an Amazon Prime/Twitch Prime subscription just to save $20 on Switch Online. But, if you already pay for Prime, this is a great deal worth grabbing while it's available.
Nintendo Switch Online is the Japanese gaming giant's equivalent to PlayStation Plus and Xbox Live Gold. It is a paid subscription service that gives you access to online, multiplayer play for many games, plus other benefits and features. You can read all about it from here.
You'll have until 28 September to redeem the three-month subscription, and until 28 January 2020 to redeem the nine-month membership.