"Dummy" (sometimes Dummy Dummy) is a common name as an error DLC for hacked Wii consoles that replaced We Can't Stop from the shop on Just Dance 2014. It happened on November 26th, 2013. This made it unavailable for people who hacked their Wii. It is apparently a Party Master Mode although We Can't Stop does not have one and they are not available for Wiis. It cannot be played.
Dummy only takes up one block on the Wii.
This can be considered the only Party Master Mode available on the Wii, and the only downloadable one at that, even though it is an error DLC.
"Dummy" is a Party Master for the Wii, according to the store.