Aftermath: Connecting the Dots between Bio G1/G2

After the final fight between Mata Nui and Teridax, Teridax was crushed by a planet, Mata Nui roams the Bionicle Universe, evil is vanquished forever, etc, etc, everyone is happy, the end. Except it isn't.

The Great Beings, seeing how ill-prepared the Matoran were against bigger threats, redesigned the Matoran Factory to build the Matoran as stronger, yet retaining their agility, which brings about the look of the "villagers". Any remaining Matoran are rebuilt. Okoto is Metru Nui, slowly reshaped over years, and renamed, as though to start a new legacy.

The Toa Nuva gain new apperances due to their Adaptive Armor still functioning, and adapting to the look of the new villagers, any other Toa remain as they are.
Ekimu was a noble, yet excellent mask-smith with an expert hand, heralding from the icy villages of Ko-Koro.  
Ekimu was hand-chosen by Artakha to bear the Mask of Creation when his eventual death came about. Makuta (who isn't related to Teridax in the slightest, there's just a heavy coincedence) was a weapon-smith from Onu-Koro, until Ekimu forged him the Mask of Control so they could work side by side, up until the events of The Legend, and the scattering of the masks.

However, below the surface of Spherus Magna, the crushed body of Teridax began leaking Antidermis. This eventually built up into underground lakes, which were found by local insectoid Rahi, mutating them into what would eventually be called Skull Spiders. The Antidermis eventually leaked to the corpses of old Toa, and reanimated their corpses into the Skull Army.