I have been thinking about the Regis for a while now, so I’ve decided to make a theory/explanation about all of the Regis. We have no idea why the Regis were created, but we do know that Regigigas was the one who created them. So, here is my theory on why the Regis were created, and what Regigigas’ goal was. The Regis were created to protect regions if something terrible happened to them, such as an apocalypse. This explanation makes a lot of sense, and I’ll start by explaining a bit more about the Regis. So, at first, Regigigas pulled continents with ropes, and showed how powerful it was. Ancient humans revered Regigigas as some sort of god-like entity and worshipped it until they eventually didn’t anymore, and sealed it away in Sinnoh. Regigigas most likely made the first trio of Regirock, Registeel, and Regice in Hoenn. The people there worshipped Regigigas until they eventually sealed away their Regi guardians. I can’t say whether or not Regigigas was there at the time, but I don’t think it really matters. Regigigas then went to the Galar Region. There, it created Regieleki and started Regidrago, but most likely fled after realizing these humans were completely hostile and didn’t want its guardians. We can see this because they didn’t want Regidrago completed, and they seemingly surpressed Regieleki’s powers for no other reason than they were afraid of it. Regigigas then travelled to Unova, and decided to go with the “if it ain’t broke, don’t fix it” approach and decided that since the previous Regi trio made humans happy while it was there, but not Regieleki and Regidrago, it decided to remake the original Regi trio in Unova, where they were once again sealed away. Finally, Regigigas moved to Sinnoh, and created its third and final trio, which were also sealed away along with it. Now, for an important point: The sealing of Regigigas is always portrayed as a forced sealing, but evidence shows that Regigigas probably allowed itself to be sealed away. It has been shown Regigigas can free itself at any time, such as in the movie “Giratina and the Sky Warrior” where it sensed the large glacier about the kill thousands of creatures and woke itself up to go help everyone. In ORAS, it leaves Sinnoh purely just to visit the Regis it left in Hoenn, possibly sensing a trainer was willing to train them. Now why was Regigigas sealed away? It was sealed away supposedly because humanity was afraid of its power. Maybe it sensed that if humanity didn’t think Regigigas could protect them and they were afraid of it, it decided to do what the humans wanted and let itself be sealed away. Regigigas moved from region to region, building guardians to protect humanity, only for the humans it wanted to protect to become afraid of all of them and seal them away. This theory doesn’t go with what is stated on Bulbapedia, but Bulbapedia doesn’t really make sense. It claims Regigigas created one trio and then the two new Regis for the Crown Tundra, and that’s it. The original trio were sealed away in Hoenn, Regigigas was sealed in Sinnoh, and the other two were sealed in Galar. This doesn’t make any sense. How were there three groups of Regis that could be encountered in the main series games in different ruins? There is also no way they could have travelled there, due to one thing or another having them being sealed away. There is also an explanation from the Multiverse theory, which explains every game is a different universe. What if in multiple groups of universes, the same Regis were sealed in different places? Well, we just don’t know, but it still doesn’t make sense in the context of Bulbapedia’s explaination. Maybe we’ll know more once the Crown Tundra DLC Releases. For now, this is the theory I’ve thought of. Are there any points I missed?
This is an interesting theory and all of your evidence seems to hold up fairly well. Personally, I always assumed that there were actually several Regigigas who worked together when moving the continents and then made their own Regi trios, but I looked it up and actually couldn't find any evidence to suggest that there was ever more than one Regigigas. In fact, finding any information about Regigigas seems to be fairly difficult, considering that there are only three unique Pokédex entries for it in the games (two of which just kept being reused).
Well, I have my own theory. It is related to Arceus. Do you know that there is no Normal plate? And Regigigas is the only normal typed Regis? So, here's my theory: Originally there are 18 different Regigigases(Regigigai?), one for each type. From the Pokédex entry of Giratina, it is banished to the distortion world. To do so, Arceus needs to fight Giratina, and possibly have not enough power to defeat Giratina, ie Arceus, the creator of Giratina, is weaker than its creation, possibly because Arceus' strongest attack has no effect on Giratina. In order to have an advantage on Giratina(ie At least allow Judgement can deal damage to Giratina), Arceus needs to somehow be able to have access to other types. To do so, it used the Regigigases/Regugugai as materials to make its plate. As Arceus is a normal type Pokémon, it did not make a normal plate, thus leaving behind the normal type Regigigas. But, Arceus fears Regigigas to take revenge on itself, it gives Regigigas the ability to create golem(the figure, not the Pokémon) like Pokémon but also place a limiter on Regigigas, forcing Regigigas to have the ability Slow Start. Regigigas then travels across the Pokémon world and created Regirock, with rock, Registeel, with metal form space, and Regice, with Never-melt ice, due to loneliness. However, as it travels the world, its creations are being sealed away due to some reasons, so it needs to create new ones. First in the location which now called Hoenn, then in now Shinno, later in Unova, and as Regigigas reached Galar. It created new variations of the Regis, with electricity and crystals of Draco energy. Regieleki is too powerful and has its strength limited by some kind of ancient technology and Regidrago, while unfinished due to lack of materials, is sealed away fearing its power will be too strong. Without any materials on hand and has its creation sealed or restricted in strength, Regigigas is very lonely and return to Shinno and has its eternal sleep. Shinno is Regigigas' last stop, it was sealed in Unova and Hoenn as well, but awoken twice due to huge earthquakes, which breaks the continents and it helped pull those back together which allow it to keep traveling. Yes, there are some flaws on my theory. TLDR: It is just Arceus killed all Regigigses and only leaves the normal types one and it creates the tri and the the new regis
