In the case of all systems on this list, recreating the Mii from scratch will functionally work, with the exception of Amiibo which do have to be transferred at least somewhere first (some DS games only supported importing from a Wii, but these are obscure and unlikely to be referenced). All Miis on this website should be able to generate instructions for every official Mii creator tool still available. The purposes of this guide will be to transfer Miis off of one of those systems to upload here, and to transfer to those systems. Recreation is an assumed possibility in all cases but Amiibo.
Unofficial Mii Makers will not be listed here. External programs to assist in loading the Miis to and from the console may be mentioned, but should not require modding the console for the scope of this guide.
DS
Miis on the DS are extremely limited. Only a few games support them, most of which are Japan exclusive. The main Mii game on DS is Tomodachi Collection, which only released in Japan.
The only known method of transferring Miis to a DS (or DSi) is from a Wii via its Mii Channel's initially hidden "Connect to DS" feature. To my knowledge, there is no supported way to export a Mii from a DS to a Wii or anywhere else, aside from recreating the Mii manually.
Activating Wii → DS Transfer
To activate the Wii → DS path, open the Wii's Mii Channel. If you don't see a DS icon, press and release A, then press and release B, then press and release 1, and then press and hold 2. After that, the DS icon should appear. This process only needs to be done once.
You can then click the DS icon to begin transferring to the DS game.
Importing in DS Games
In Tomodachi Collection, you can import Miis from the Wii via the option in Town Hall after you have made at least three Mii residents on the island. In every other game, the option will be found shortly after entering the game or in Final Fantasy's case unlocking the item that allows this transfer to be done. You will be looking for an option to Import from Wii.
Wii
Transferring Miis to and from the Wii is, to me, one of the most thematically fun as the vehicle for doing so will be the Wiimote.
To start, open the Wii's Mii Channel. You will be looking for the Wiimote icon in the top right. After clicking it, select the connected Wiimote you would like to take Miis on and off from. Here you have ten slots where you can rearrange Miis. If your goal was to take Miis to the system, this is where you will do so. To take Miis from the system, go ahead and place any Miis into the Wiimote slots, making sure to remember which slot from left to right the Mii was placed in, save, and then power off your Wii.
I will likely research and see how difficult it would be to make my own program to streamline this process, but for now this is what it looks like.
Transferring via PC (Windows)
You will need to pair your Wiimote to your Windows device. This can with some models be done simply through bluetooth settings and putting the Wiimote in sync mode, but the most consistent method I've found is simply to pair the Wiimote in Dolphin, and once it is paired, leave Dolphin running but we won't be using it further.
You can then use WDML Mii Transfer. After unzipping the program, with the Wiimote paired, you can use readslotX.bat to transfer a Mii off of the Wiimote and to your device, where X is the slot the Mii you wanted to read was in, minus one (so if the slot was the third from the left, use readslot2.bat). To write a Mii to the Wiimote, first place the Mii file in the same folder as the WDML files. Rename the file miiX.bat, where X is the slot you want to write the Mii to, minus one (so if I wanted to write to the fifth from the left, I would name it mii4.mii). You can then run writeslotX.bat, where X is the same number from miiX.bat.
Transferring via 3DS
If you have a 3DS, and you're just looking to transfer off of the Wii, the recommended option would be to transfer to your 3DS and use that as your way of getting it off of the console. First open the Wii's Mii Channel. If you don't see the DS icon on the right side of the screen, press and release A, then press and release B, then press and release 1, and then press and hold 2. After you do this, the DS icon should appear and you can press it. On the 3DS, open Mii Maker, then select "Send and Receive". Tap "Receive from Wii" and follow the prompts on both consoles. You should be able to freely send Miis to the 3DS from here, but not to the Wii. To write to the Wii, you will still have to use the method with a Windows device for now.
3DS
The 3DS is the easiest console to work with when it comes to transferring Miis. It can get Miis from the Wii (see the Wii section), uses QR codes, can upload straight from its web browser, can scan QR codes easily, can write to Amiibos if you have the NFC Reader accessory OR a "New" 3DS (required for directly transferring to and from the Switch/2), and is compatible with Special Miis. The 3DS is, in my opinion, the best console for interacting with Miis.
Exporting Miis from 3DS
To take Miis off of the 3DS, simply open Mii Maker, select "QR/Image Options", and then "Save Mii as QR Code". Select the Mii, and that's it! The QR code will be displayed on screen and can be scanned by another device using this website. You can also find the QR code file in the DCIM folder on your 3DS' SD card, or open this website in the 3DS Internet Browser and upload the image file from there.
Importing Miis to 3DS
To get Miis onto the 3DS, simply display the QR code using another device. Open the Mii Maker app, then press "QR Code/Image Options", and then "Scan QR Code". Hold the camera up to the QR code, and you're done!
To transfer directly with the Wii U, see the Wii U section.
Wii U
Everything said in the 3DS section about working with the QR codes also works on the Wii U in pretty much exactly the same way. The one caveat to note is that if the Mii is considered a Special Mii, the Wii U will be unable to interact with it.
Direct Transfer with 3DS
To communicate and transfer directly with a 3DS, open both console's Mii Maker and select "Send and Receive". On the 3DS, select to communicate with the Wii U, and on the Wii U, select to communicate with the 3DS. Once connected, Miis can freely be sent in between.
Copying from Wii Mode
To send all Miis from the Wii mode of the Wii U to the Wii U's Mii Maker, select "Send and Receive" and then "Copy from Wii Menu". This will copy all Wii mode Miis to the Wii U mode Mii Maker at once, and Miis cannot be sent in the other direction.
Amiibo
Amiibo are going to get their own section due to being the only unmodded mode of transport with the Switch/2, and being able to be interacted with via the 3DS and Wii U as well. Each Amiibo can hold a single Mii, and do this by registering an owner of the Amiibo.
Using Amiibo with 3DS
On the 3DS open the home menu settings (the icon on the top left of the home menu on the touch screen) and select "Amiibo Settings". You can then scan your Amiibo, and follow the prompts to register or change the Mii associated with the Amiibo. You will need either a "New" 3DS/2DS, or an NFC Reader accessory.
Using Amiibo with Wii U and Switch/2
To transfer off of both the Wii U or Switch/2, open System Settings. Find and select "Amiibo Settings". You will then want to either Register or Change the Owner of the Amiibo, and you can then load your Mii onto the Amiibo from there.
On the Switch/2, open Settings and find the Mii menu. Select to Create a New Mii, and then Copy Mii from Amiibo. Tap your Amiibo, and the Mii will be transferred.
To my knowledge only the Switch/2 can copy a Mii from an Amiibo.
Using Amiibo with Phones
Amiibos can be interacted with using NFC enabled phones.
Android: Tagmo
To use Tagmo after selecting your Amiibo key files, press the "nfc" button in the bottom right, and then "Create Backup". After scanning your Amiibo, this will create a .bin file representing the data your Amiibo transmits. This file can be uploaded to our Amiibo page to interact with further.
To write to your Amiibo, place the new .bin file in Tagmo's folder. Making sure the filename is right on Tagmo's main screen (you may need to drag down to refresh), tap it and then tap "Update". Scan your Amiibo once more, and the Mii will be available on the Amiibo.
iOS: Reddit Thread with a List of Options
There is no known really good option for iOS. All I am aware of are paid, or limit the amount of writes you can do before paying. If this ever changes, please feel free to contact me at the link in the footer. For the time being, the linked Reddit thread lists some options you can pay for, or wade through the limited free writes on. I use an Android as my primary phone, so I use Tagmo and have no use for paid iPhone apps. If a free option becomes available, let me know and I will become acquainted with its use and add it to this guide.
Switch/2
The Switch is the most isolated the Miis have ever been, and can only transfer Miis with other Switch/2s, OR by using an Amiibo, which you can read more about in the Amiibo section.
Transferring Between Switch/2 Systems
To transfer a Mii between two Switch/2s, open the System Settings, then the Mii menu, and find the Send/Receive and "Search for Users to Connect With" options. Once both Switch/2s do this, you can connect them and transfer freely.
Mii Studio
Mii Studio is Nintendo's online offering that exists primarily to provide profile pictures for your Nintendo account. After making sure your device is logged into https://accounts.nintendo.com/, you can open Mii Studio here.
Using Third-Party Tools
To transfer Miis in and out of Mii Studio without direct recreation, you will need a tool of some kind. This browser extension by HEYimHeroic is able to help with this. After installing, go to Mii Studio, edit a Mii, and make sure to make a small change even if you revert it right after. Once you do this, open the extension and copy the generated data. On InfiniMii, use the Copy Hex or Copy Base64 export options when you need portable raw Mii data.
Site Summary: InfiniMii is a searchable database and toolkit for Nintendo Mii characters, including browsing, downloads, QR codes, conversion tools, transfer guides, and official Mii preservation.
