What you will need
(Note: you can connect to online with Champions with an original DS or DS Lite but you'll need a WEP connection or open connection)
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Nintendo DS or DS Lite: Open Fossil Fighters: Champions, access your save file, select “Multiplayer”, and select “Settings.” (If you have previously accessed the Nintendo WFC with Champions before, you should first select “Options” and then “Erase Nintendo WFC Configuration.”) Select “Nintendo WFC Settings” and either create a new connection or modify an existing one. The SSID will be the name of the connection you’re accessing. If the connection has a password, enter it, otherwise leave the field blank. Next, scroll through the options until you find “Auto-obtain DNS” and set it to “No.” Set the Primary DNS to 167.235.229.36 and set the Secondary DNS to 001.001.001.001
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Nintendo DSi family: Open the System Settings, then select “Internet” and “Connection Settings.” Select the connection file you wish to edit, then “Change Settings.” Set “Auto-Obtain DNS” to “No,” then select “Detailed Setup” and set the Primary DNS to 167.235.229.36 and set the Secondary DNS to 001.001.001.001
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Nintendo 3DS family: Open the System Settings, then select “Internet Settings.” Select “Connection Settings” (not “Nintendo DS Connections”). Select the connection file you wish to edit, then “Change Settings.” Select “DNS,” and under “Auto-Obtain DNS,” select “No.” Finally, select “Detailed Setup” and set the Primary DNS to 167.235.229.36 and set the Secondary DNS to 001.001.001.001
・20100... It is possible that you have the wrong DNS.
If rechecking doesn't help, try setting your secondary DNS to either "164.132.44.106" or "1.1.1.1". (This probably won't work cause the codes are probably outdated or are just the current ones)
・20110...I have written a long list of solutions here. It could be a server-side problem, so if you can't solve the problem, you can wait a day or two.
・2388y...y days later, you can play online.
・238xx...xx hours later, you can play online.
・40000～49999... Unknown.
・51100～51199... WEP key may be wrong.
・52000～52099... DHPC error. The SSID of the access point or the password for it may be wrong.
Or, you may be able to connect to it by trying several times while taking some time.
If this does not solve the problem, the cause may be that you have a number of different devices connected to your router.
In that case, you may be able to increase the number of devices assigned to the router. Or, you may be able to connect by creating a fixed (manual) IP address.
I don't know much about this, so please try searching for "3ds 52000".
・52100～52199... you may have the wrong DNS.
If rechecking does not help, try setting your secondary DNS to either "164.132.44.106" or "1.1.1.1".
・52200～52299... The connection test failed, please restart your DS and try again.
It's a donation-driven server, so sometimes things go wrong. Either your router is broken or you are not connected to the Internet.
Or, you have a very poor Internet connection.
・54000～54099... Either your router is broken or you do not have an Internet connection.
Or, you have a very poor Internet connection.
・60000... Cannot connect to Wiimmfi with that file. I'm not sure, but it seems that the Friend Code is not supported.
If you delete the file, take over the reviver, and start over, it may work. (In short, you need to reacquire the Friend Code.)
If you are using the DS or DS Lite and DSi series, you can use the "Delete Nintendo WFC Configuration" function, so you can easily reacquire the Friend Code without deleting the file.
The caveat to this feature is that it will erase all of your online battle records, friend lists, your own friend codes, and Internet connection settings in the data of that DS.
The way to get to this feature is,
System Setting
↓
Internet
↓
Options
↓
Delete Nintendo WFC Configuration
・61010...This is a communication error with the Wiimmfi server. This is often a problem on the server side, so wait until they fix the problem.
・71010...Delete all your friends from your friend list and try again. Alternatively, delete any friends that have a non-Wiimmfi compatible friend code.
・84020...This is most likely caused by a bad communication environment.
Or it means that the Wiimmfi server is down.
・85020... This is most likely caused by a bad communication environment.
Or it means that Wiimmfi's server is down.
I can't answer that because I don't have any details about how to resolve the error codes. So, I put the list and the URL of the error code search.
Error code List↓
Error code retrieval↓