ok, makes sense Also mentioned other things you need to cover.
Lastly for pendants and Necklaces, when GX first started Jaden, Chazz, all the academic students were given certain necklace to hold on to to keep safe from the Shadow Riders. This might fit for pendants or Necklaces. They were the key to unlock the Sacred Beast cards.
Then for impostors, Alister during the Seal of Oricalcos, he copies the identity of Pegasus to duel Kaiba, but revealed himself during the middle of the duel. "Alister's the name Kaiba boy" - my god I love it when he said that lol.
And to add "Sacred Temple".
Now that I remembered on Yugioh R you have seen many sacred Temples relics of either Egyptian Gods or Yugi and Kaiba rivalry in the past.
In Yu-Gi-Oh! GX I think it was the part where Adrian had the Exodus power and going back to his lair, or something of some sort about the Underworld. Memory is still haze, about GX for now. Or to think of it it might have been during Marcel. When Yubel had embodied Marcel, and went looking for the Sacred Beast. The Underground place where they were hidden didn't look normal, but I don't have an exact picture how they looked liked.
Yu-Gi-Oh! 5D's it's the beginning, when Goodwin brings the 5 signers to his Sacred Temple showing the signs of the signers, and past relics of the Crimson Gods and the Earthbound Immortals.
Yu-Gi-Oh! Zexal, somewhere they showed you a scene of his dad traveling and fall in, and received the pendant. Just outside the door, when you enter the Emperor's Key is a part of Sacred Temple shown the difference of an ancient world exist. The thing that Astral is on all the time is just a mechanical spaceship. Sorta like an alien who lost gas and stranded out in the desert. But the door shows a weird symbolic sign, so that's part 1 of the mystery.