Lots of questions that get answered over an over, and lots of pointless/troll posts. Hopefully this FAQ will help us cut down on all the nonsense. This FAQ is ONLY for the NEW 3DS, not for an Old 3DS, even if you buy a new Old 3DS.... NOTE: Big thank you to Breith for helping me make this FAQ a lot less confusing. -------------N3DS flashcart FAQ-------------Q: What flashcart can currently be used on the New 3DS?A: As of now, only the SKY3DS (and now Gateway as long as you a physical copy of OOT or CN) can be used with a New 3DS. Moreover, you can be on ANY current firmware (up to 9.5.0-22), and your Sky will STILL work on it.Please note that Sky will not allow you to play region free games, nor does it (currently) have eShop ROM support - you have been warned.Q: What about firmware? I hear Gateway works for 9.2 (and lower) N3DS's?A: Check the excellent firmware thread here. Big thanks to marksteele for creating and updating it.Q: But I heard the Gateway worked on the New 3DS without the need of anything else?A: Not right now.Q: But when?A: Maybe eventually ® is what I will say.Q: What is this header thing? Privates headers? Public headers?A: Short story: The header is something that "tags" your game for online multiplayer. Public header are freely distributed on the Internet, while private ones are not.Further reading: Each 3DS game has a unique header. A team releases templates where each game is assigned a header. When people use them, they are also unknowingly using this header. Nintendo sees thousands of people play a game with the same header, and ban their N3DS. It's really that simple.Q: Well... OK. And how can I avoid ban?A: Use a private header from one of your games.Having said this, we cannot attest that Nintendo will still not ban you. They just haven't until now.For all we know, all flashcarts are easily detectable.To get more information, see the More on Headers section of this FAQ. Q: How do I get a header that isn't public knowledge? I want to use my own unique private header.A: Easy. Rent, borrow, or buy a retail game, then follow the steps outlined here.Be sure to thank Cyan for his guide. Please note that you need to use an O3DS for this. Anything 4.5 (and over) and 9.2 (and under) should work.Side note: Buying (or borrowing) a game is wiser than renting one. If too many people rent the same game (from the same place), the header will not really stay "private" for a long time.Contrary to popular belief, you DO NOT need a Gateway to get a private header from a 3DS game.Q: How can I inject a private header into my game? I heard I need a Gateway to do this.A:This is common misinformation floating around gbatemp. Other tools exist, like the great multitool (thank Foxi4 for his work), which you can use to make your own .3DS ROM templates.As an alternative, No Ban no Sky by hackotedelaplaqu can also be used.Q: Do I have to upgrade my N3DS to the latest firmware to play games online?A: No. You simply need to have a ROM with the latest version (revision) of the game.Side note: To update the game, you most likely need eShop access (unless you can find another revision online - one that includes the latest patch).Q: How can I access the eShop?A: You will need the last sysNand (or firmware) available. Be aware that a sysNand above 9.2 will not be usable on Gateway (if they ever support the N3DS).Q: Any point in upgrading my N3DS firmware?A: No - at least not if you can avoid it. Basically the older your firmware (sysNAND) is, the more potential flaws you have. And these flaws are used as entry points for exploits/flashcards.Q: So what flashcard should I get?A: Well, the Sky3DS is the only one that works on N3DS FW <9.2 now. Gateway may work eventually, and a new (most likely hybrid) card named DSTWO+ is possibly on the horizon.Q: Hybrid?A: It will most likely will have built in emulation of other Nintendo handhelds/consoles. We have no confirmation on if it will work with the N3DS.Q: What SD card should I use in my N3DS or flashcart for maximum compatibility?A: This is what I use. It's a 64GB SanDisk card and I have not had a single issue with it.Although honestly, your best bet is to go online and find the cheapest name S brand (SanDisk, Sony, Samsung) to buy. As long as it is at least class 6, you shouldn't have any issues.Lexar and Kingston work as well.I personally had problems with PNY, Transcend, and OV - although a lot of people consider them to be "good".Stay away from anything I didn't mention in this answer, as odds are that they are cheap Chinese junk.Q: I want to play NDS games, what DS flashcart works on the N3DS?A: We have reports that the DSTWO and R4 RTS work fine. Credit goes to these users: nyder, joeh1974, and cutterjohn.Q: So wait, is homebrew possible on the N3DS?A: Soon ®. Check out the Special Note section below. Thanks to KARL3DS, you can use the Cubic Ninja exploit (even right from your Sky3DS card). This exploit only works on 9.2.0-20U and lower N3DS handhelds.Further reading:More on Headers: So as I said before, each 3DS cart has its own unique id (header), and if we look at 5 Bravely Default carts, we will have 5 different headers. Now within these 5 Bravely Default carts, the headers will be somewhat similar.Now if we compare these 5 Bravely Default carts to 5 Monster Hunter carts, we will see that the headers for them are pretty different, BUT the 5 Bravely Default carts have quite a few similarities between each other, as do the Monster Hunter carts. However, the Bravely Default headers have very little (if any) similarities with the Monster Hunter headers.To reiterate - carts of the same name will have more in common with each other than with carts that do not bear their name.What this means is that there is very likely a set list of headers for each 3DS title, and if you go online with a Monster Hunter ROM, but use a header for Bravely Default - it may be detectable. Then, a safer way to go online is to use a private header and a private header from the same game. So Monster Hunter will use a header from another Monster Hunter, etc.Having said all that, no one has reported being banned after using a private header from whatever game they want (for the moment).Update: A close friend of mine has been banned for using a Gateway and playing with an OOT header while racing in MK7. That is the ONLY game he played online, and he used the OOT header for it. Having said this - he did play quite a few games offline, with the default public headers.Special Note: Be sure to check out [WIP] KARL3DS. They have been making incredible progress, and are actually running code already (Hello World type stuff)!While piracy will (most likely) not happen from this, homebrew (and hopefully some solid emulation) will.