>>51360309Zygarde is made of stones like all the giants and the Original One family, which are the only pokemon capable of losing pieces and dividing in other pokemon yet still be alive and as individual life forms or hive mind in the case of Zygarde (although it's for all of them, cause even though Reshiram and Zekrom became its own thing, they still feel each others and Kyurem's pain)
which also confirms that the space stones in Kalos and those in Hoenn including the key stones, the giant key stone and the ultimate weapon, are pieces of zygarde
The giants are in pieces and lose pieces because as the plates inscriptions state they were destroyed by the Original One which also used their powers to create the universe, moment in which the pieces of the Giants, the Original One included that impaired itself just so it could have its space, time, antimatter
Zygarde's room cave represents the place where its original gigantic body (at least what of it fall on earth, supposedly the size of Eternatus which is far from its complete body and probably not even Eternamax is complete) fell, since it got the shape of 100% cells Zygarde's wings and it's in the first floor, also in Generations they showed it being an open wide crater.
There's proof of OG dragon kyurem being gigantic too, which confirms the connection, although the only one that didnt get an explorable giant crater was Necrozma, the other characteristics in common with Kyurem/zygarde/Eternatus and Totem pokemon becoming bigger through his power confirms its gigantism too
