Small update: the next chapter will be coming out later next week. There will also be a small retcon on how some cards work, along with the introduction of card rarities into the story. This will affect some of the MC's cards.
First are Ghost Rares. These are cards that are tied to one person, and no other copies of these monsters can exist as long as the current monster exists. For example, Kaiba's three Blue-Eyes are tied to him, along with Mister Moto's one Blue-Eyes. There can never be more than four copies total.
This also affects the Ash Blossom that the MC has. She is the only version that exists in that world. The same will apply to all the other Ghost Girls that appear in the future.
Next, all Divine monsters and most Level 10 monsters are Overframe cards, along with any monsters strengthened by the bond they share with a powerful duelist. For example, Dark Magician with Atem or Dark Magician Girl with Yugi. This shows that the monster can manifest without the help of a human.
This affects the MC because the Three Wicked Gods and Underworld Goddess are all Divine monsters, so they are Overframe cards. This would also apply to the Sacred Beasts and the Egyptian Gods.
Please let me know if you think the Signer Dragons should also be Overframe cards, and if you have any ideas for other rarities for the future.