Nintendo's NES Classic Edition ships with 30 of the most beloved games for the system, though there's no official way to add more titles once you're tired of beating Super Mario Bros. 3 for the 10th time. If you're willing to get your hands a little dirty, however, you can hack the retro console's software and add just about any NES title you want, provided you can find the ROM file for it.
As discovered by the folks at the NESClassicMods community on Reddit, adding games to your NES Classic doesn't require you to crack open your system or use any physical tools. However, this hack can brick your system if performed incorrectly, so proceed at your own risk.
You can find the full steps for the hack here or in the video below, but it basically boils down to this: First, make sure you've made a save file for Super Mario Bros. in the first save slot. After that, you'll need to connect your NES Classic to a computer via microUSB and boot the system in "FEL" mode, which you can do by holding down the reset button while turning the power on. While this is happening, you'll need to be running a "sunxi-FEL" interface on your computer, which you can learn about here.
From there, you'll have to essentially create a directory where the ROM files and cover art for any of your added games will go. You'll have to seek out ROMs for whichever games you want to add yourself, which can be legally dicey. According to Nintendo's legal website, "it is illegal to download and play a Nintendo ROM from the Internet." Again, you're operating at your own risk if you perform this hack. However, there are a number of legal, open-source NES ROMs that you can find with a bit of digging.
If you follow the steps correctly, your new games should show up in the main menu the next time you boot up your NES Classic. Most users in the original Reddit thread claimed that this method worked well for them, with one person claiming to have added a total of 40 additional games to the system.
Considering that the NES Classic is essentially a miniature PC wrapped in a nostalgic plastic shell, it's no surprise that it can easily be cracked into and modified — as long as you're willing to risk your system, that is. There are plenty of other retro consoles that play tons of classic games without the need for any fancy software hacking, so be sure to check out our roundup of NES Classic alternatives.