Some technical details as well as the games that support it were confirmed.
Details regarding the 3DS's Second Circle Pad attachment were revealed today.
While nothing was said during the actual Nintendo 3DS Press Conference, an update on Nintendo's site confirmed some new details regarding the peripheral. It requires one AAA battery to work.
The Circle Pad (Slide Pad in Japan) attachment will be released in Japan on December 10, 2011 and will retail for 1,500 Yen. It will only work with games that carry the Circle Pad icon on their boxes.
In addition, a list of the games that use the peripheral was also released. The games that use it are as follows:
Monster Hunter 3G - 12/10/11
Biohazard Revelations - Early 2012
Metal Gear Solid - Winter
Ace Combat - Winter
Samurai Warriors VS - 2012
Kingdom Hearts 3D - TBA