A little backstory of the original Kamen Rider OOO have been revealed. The events were dated back 800 years ago (1210) wherein Kamen Rider OOO, with immense powers, fights the Greeeds and sealed them.
800 years ago, Kamen Rider OOO could freely use the Core Medals at will, and could change combos and achieve unbelievable powers. No one ever knew and can explain those powers are. Will OOO's powers ever be explained in the current timeline?
Each Greeed have their own characteristics and differences: Uva which have powerful physical strength, the strategic Kazari, the full of greed and easygoing Gamel, and the one who creates the most Cell Medals and gives them out, the only female Greeed, Mezool.
The Greeed Gamel seems to look up onto Mezool as a motherly figure. It is stated that he is willing to risk his own life for her, and even approaching Kamen Rider OOO.
Kamen Rider OOO RaToraTa, a form which utilizes Raion (lion), Tora (tiger) and Cheetah Core Medals from Kazari, will debut in the next few episodes against the Shark Yummy. This Yummy comes from, nonetheless, the water-based Greeed, Mezuru, is very similar to the piranhas and appears in large quantities.
Using the RaToraTa Combo, Kamen Rider OOO's whole body is able to emit powerful heat rays (which could be this combo's Scanning Charge). These heat rays causes the rivers nearby to evaporate which makes it super effective against water types.
And now, here's the guy that we are waiting for! He is Kiyoto Maki (Yuu Kamio). He's the head scientist of the Kougami Foundation, the guy who is behind the foundation's Medal System and the Candroids that Kamen Rider OOO is using. According to an existent rumor, he Maki is creating a new Medal System using Core and Cell Medals which could lead to the Rider System that will be later used by this year's 2nd Rider.
Note: The info revolving his involvement with the 2nd Rider is still a rumor. Please take as a grain of salt. Thanks!
Source: alternate-Zer0 and DecaEnd