The eyebrow-raising 3DS second circle pad attachment will cost 1500 Yen (£12.30) and be released on 10th December in Japan.
Monster Hunter Tri G won't be the only game that supports it.
Nintendo has revealed five other compatible games: Resident Evil: Revelations (early 2012), Metal Gear Solid Snake Eater 3D (winter), Ace Combat 3D Cross Rumble (winter), Dynasty Warriors Vs (2012) and Kingdom Hearts 3D (TBC).
The 3DS second circle pad requires one AAA battery to run.
Games that support the second circle pad will display an icon showing the attachment.