Install Shark for Root on your phone.
Fire up your favorite mobile hotspot app on your phone.
Launch Shark for Root and edit the parameters to append -i wlan0 to the end. The final textbox should look like this:
-vv -s 0 -i wlan0
Case is important, so make sure all the letters are lowercase and the spacing is exactly like the text above
Hit the start button in Shark for Root, then connect your Wii/DS to your phone's mobile hotspot.
Play online and capture some packets!
When you're done, hit the stop button in Shark for Root. A .pcap file should be either in your internal memory or SD card.
Every Android phone is different, and some phones might not work, even if they are rooted. If everything seems to work but the .pcap file is empty, your wireless interface on your phone might have a name that isn't wlan0. You can try replacing that part of the parameter textbox with eth0 and might get captures that way. Worst case you can just leave the -i wlan0 part altogether and capture all traffic on your phone, but you will have to filter out phone traffic afterwards.