OOO's gimmick revolves around his mix-and-match body. While one medal can only become one portion (A head medal is only a head, etc), he can freely swap various medals to change that portion of his body.
While there are only 6 official combos (The combos use medals of one solid color) in series, one of which can't swap medals, he also has 3 movie exclusive forms, one variant form, one Combo that he never actually used (The Black medals), and 3 medals that weren't actually used in the series or movies (The 2 Kangaroo medals and the Panda medal).

He has that many 'potential' forms. Not nearly that many were ever used though.

i did steal my number from KamenRiderOOO though. So if it's wrong, blame him :)

You know, I totally forgot about Ta Ma Shi. :lol

How could you forget about Khamahamaha form?

However, when it comes to that number, the following have to be disregarded in terms of Figuarts: PuToTyra (Never (And, in series, I don't think it can be) used outside of itself), BuraKaWani (Like PuToTyra, medals only used for itself), Super TaToBa, Imagin core, Shocker core, and both Kangaroos.

The only medals that were mixed and matched to make forms were the ones used in the 5 base combos (TaJaDor, ShaUTa, GataKirBa, SaGoZoh, and LaToraTah). Everything else, while possible to be used in the belt, wouldn't get a Figuart (Outside their own combos).

I think, just using the base 5 medal types, there are 125 possible combinations(?) If I did my permutation calculation right. So ~128 not using the 2 Kangaroo medals.

So, with 125 possible in series combinations, plus the other forms used in series or movie (PuToTyra, Super TaToBa, BuraKaWani, TaMaShi, and TaToBa purple eyes ver.) leaves OOO at around 130 Figuart possibilities.

Possibly more, should Eiji ever get to use the Future or the Black core medals in a future movie or if Eiji ever mixes the Orange cores with others.

Right now:
Kabuto
Dark Kabuto
Hyper Kabuto
TheBee
Gatack
Kick Hopper

I only ordered Kick Hopper on a whim, and i regret it, I haven't even opened it. Though I'm sure I"ll be come more interested in him, Punch Hopper, the Zectroopers and movie characters once I see more of the show.

Count yourself lucky.
Kickhopper is one of the most wanted Kabuto Figuarts.