According to the link below, the second Rider of Kamen Rider OOO uses a gun to transform.
The link is currently down. However, according to people who say they saw the content it says
"The second Rider's Transformation Gun! 3 O Medals are included, these medals are used to transform when they are put inside the gun. By switching out medals you can change forms. You can also activate various special attacks with Cell Medals. Cell Medals are not included with the gun."
Another toy site has mentioned the toys of a second Rider. On that site it stated that this second Rider uses guns as his main weapon. However, this link has been taken down as well. Luckily, it's available through cache. http://www.igaya.co.jp/?pid=23791807
This link says that a belt and a gun is included. The belt works together with the gun.
This could mean that the rumors regarding the second Rider uses guns mainly. In case you haven't read the rumors, here they are.
"The second rider is called Birth (It's just my romanization, the original post said バース/Baasu. Though the origin was from the word "Birth" according to the same post.)
He uses guns mainly.
He uses guns mainly.
He is able to use gachapon capsules and get weapons and other items from it. They work similarly to the Candroids.
It's also rumored that the 3 main medals he'll be using is Kabuto, Bee and Dragonfly. By using the stacking trick to activate various medal sounds on the O Driver, the bee (hachi) sound has been heard. Kabuto and Dragonfly on the other hand, are still unknown.
