Attention Nintendo Switch owners: Starting this week, most games will lose online functionality unless you pay for a new service

• Starting Tuesday, September 18, Nintendo's Switch console will require users to pay for its online service in order to play games online.
• The service, named "Nintendo Switch Online," costs $20 per year.
• In addition to enabling online co-operative and competitive play, Nintendo Switch Online offers access to a growing library of classic Nintendo games.

If you're one of the over 20 million Nintendo Switch owners, take note: Nintendo's about to lock online play behind a membership paywall.

Starting on Tuesday, September 18, Nintendo is launching "Nintendo Switch Online" on the Nintendo Switch. The service costs $20/year, and primarily offers access to online gameplay - the kind of online gameplay you've already been enjoying for free on Nintendo's consoles for years.

Since the Nintendo Switch launched in March 2017, playing games online has been free. Games like "Mario Kart 8 Deluxe," "Splatoon 2," and "ARMS" that all launched in the first six months of the Switch's life - games that are primarily played online - will all require the $20/year service to be played online.

Nintendo's upcoming "Super Smash Bros. Ultimate," arguably the biggest game Nintendo is launching this year on the Switch, will also require Nintendo Switch Online in order to be played online.

There's one notable exception in "Fortnite," which won't require a paid account to be played online, but few games are exempt: Hit third-party games like "Minecraft" and "Rocket League" will both require the service if you're playing online (even co-operative online play in "Minecraft").

For $20/year, Nintendo's offering a handful of other benefits with Nintendo Switch Online. 

As Mario demonstrates above, the service consists of five primary components:

1. Online multiplayer, both co-operative and competitive.
2. A classic game library, starting with 20 Nintendo Entertainment System games.
3. Cloud save support for "compatible games."
4. A smartphone app that provides voice chat support for online multiplayer.
5. "Exclusive special offers," starting with the ability to purchase wireless NES-style gamepads for the Switch.

The service is similar to those offered by Sony and Microsoft on the PlayStation 4 and Xbox One - PlayStation Plus and Xbox Live Gold, respectively.

Those services also offer access to online gameplay, provide a growing library of free games, and enable cloud saves.

On paper, Nintendo Switch Online is nearly identical to Xbox Live Gold and PlayStation Plus. In reality, Nintendo Switch Online is actually much better than both Sony and Microsoft's offerings in one key way: Price.

At $20/year, Nintendo Switch Online is by far the least expensive online subscription service for a game console; PlayStation Plus and Xbox Live Gold cost $60/year each.

But there's a crucial difference between what Sony/Microsoft offer and what Nintendo is offering: Far larger libraries of free games. Both Xbox Live Gold and PlayStation Plus offer free games each month, and we're not talking about games that came out 30 years ago or more. Games like "Destiny 2" and "Rocket League," among many other blockbusters, have shown up on both rival services. 

In so many words, $60/year is a lot to pay for an online service, but both PlayStation Plus and Xbox Live Gold pay for themselves in the first few months through free games.

In the case of Nintendo Switch Online, the free games included are from the Nintendo Entertainment System - Nintendo's first major video game console, which played games like the original "Super Mario Bros" and the original "The Legend of Zelda."

They're being updated with online multiplayer, and can be played on Nintendo's latest hardware, but these are otherwise the same classic games you've played many times before on previous Nintendo consoles.

Here are the first 10 games: "Super Mario Bros. 3," "Dr. Mario," "Balloon Fight," "Donkey Kong," "Ice Climber," "The Legend of Zelda," "Mario Bros.," "Soccer," "Super Mario Bros." and "Tennis."

Nintendo says that 20 classic games will become available for download when the service lights up on September 18, and a recent video Nintendo published hints at what those other 10 initial games might be: "NES Open Tournament Golf," "Solomon's Key," "Double Dragon," "Excitebike," "Ghosts and Goblins," "Super Dodge Ball," "Baseball," "Pro Wrestling," "Gradius," and "River City Ransom" all make brief appearances.

Additionally, "Tecmo Bowl" and "Yoshi" have appeared in promotional images - a hint at what's to come, perhaps.

Nintendo Switch Online goes live on September 18, and will require a system update to version 6.0.0. Whether you download the update or not, games like "Mario Kart 8 Deluxe" will stop working online without a Nintendo Switch Online paid account as of this Tuesday.

You can watch an overview trailer of Nintendo Switch Online below:

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