It's dubbed the "3DS Kakuchou Slide Pad" or "3DS Expansion Slide Pad". It's real. And it's truly an ugly product—the ugliest since the original Nintendo DS. The lackluster looks are a shame because the 3DS is so pretty. There's more than looks to this, though.
The 3DS Expansion Slide Pad is less a simple add-on and more a cradle for your 3DS. It not only adds extra buttons: The peripheral also supposedly has R1 and R2 buttons, and definitely appears to have an L2 button. There is no L1 button.
It looks like some sort of peripheral that one would grip.
Since it is a cradle, it does surround certain parts of the 3DS. It appears that the game cartridge slot is blocked by the 3DS Expansion Slide Pad, meaning that you must take the 3DS out of the Expansion Slide Pad to change games. Apparently, the wireless switch is also blocked.
The infrared and battery port are not blocked. The front headphone jack is also not blocked. The front also appears to have little slots so the 3DS' colorful power lights are viewable.
This is an ugly bit of Nintendo kit. Even though it is horrid looking, it actually might feel solid in the hand and play well. It depends on things like its design and what kind of material Nintendo used.
No matter how it looks, the the 3DS Expansion Slide Pad is surely just a stopgap on the way to a better, sleeker 3DS iteration. You thought this time was going to be different, early adopters?
F1188 3DS「モンスターハンター3(tri)G」[カプコン] [■■速報＠保管庫(Alt)■■]