The Ten/Nine Dragon Gods are a group of originally ten tremendously powerful Dragons that inhabit the northern continent of Guiltina, with the remaining nine after the death of Dogramag each stated to rival the might of Acnologia. 

The Ten/Nine Dragon Gods have existed since the year X633 at the latest, the same year that the first Magic Guild, Magia Dragon was created. They gained the description of "gods" due to the fear they struck in the humans who overheard their evil deeds over time, as well as each individual Dragon's insurmountable strength, said to rival (and later surpass) that of Acnologia, one of the most powerful and feared beings in Earthland. 

The Tenth Dragon God, Dogramag, was considered the weakest of the group but still an overly strong Dragon compared to his peers in the magic world.

In the past, the Ten/Nine Dragon Gods fled to Guiltina in order to escape Acnologia, only to later figure out that their powers continuously grew even beyond the Dragon King himself. The dragon gods remain stationary unless something "big" occurs, upon which they could potentially create a calamity. Consequently, due to the possibility of them clashing and mutually killing one another, they all kept each other in check through these means given another party could gain something from their demise. 

Because of their hidden existence and lack of involvement in the Dragon King Festival, very few people have known of their existence; among those who are aware are a select few in the Magic Council. 

The Ten Dragon Gods have not all met together at once, leading them to not know everything about one another or even their whereabouts, given that Mercphobia himself did not know much of anything of Viernes. 

The Eight of them are all implied by Ignia to possess a form of Transformation Magic, allowing them to assume a human form with a likeness to their Dragon counterpart, albeit weaker but still at a high-tier of power. It has been noted that while Dragons have the ability to transform to an extent, it is not as common given powerful Dragons such as Igneel never used Transformation Magic. 

1. Y/N Rose Dragneel A.K.A. the Demon Dragon God. One of the two Dragon Slayers to reached the title of "Dragon God", Y/N was consider to be the strongest among them due to his mastery of all different types of Dragon Slayer Magic. He's also known as the Demon King or the Soul King for creating his own army of demons, machines, Arrancars, and Quinces. His desires are to rid the world of Salem and Acnologia and create a world full of demons, dragons, and machines. He also wants to kill humans and Faunus not because he hates them, but simply because he's judged them to be inferior, foolish races that only exists to hate and kill each other, and has no place in his designs for the universe. 

(human form) 

(dragon form) 

2. Ignia A.K.A. the Fire Dragon God for his intense fire. The son of the Fire Dragon King Igneel, who fostered the orphan child Natsu in conjunction with Zeref's plan. The Fire Dragon God, Ignia, holds the highest authority as the Guild Master of the Dark Guild, Fire and Flame. His biological relation to the Fire Dragon King, Igneel, and his foster brother, Natsu Dragneel, adds to his significance. His leadership is marked by his sadistic nature, callous demeanor, and his mastery over Fire Dragon Slayer Magic. He's also Y/N's friend and rival. He also wishes to challenge Natsu to a fight to the death to test his own strength.

(human form) 

(dragon form) 

3. Mercphobia A.K.A. the Water Dragon God for his voluminous water capability. A large serpent-like Dragon who controls the Water Capital of Ermina and is worshipped as a protector god to its citizens. Once a ruthless killer of humans, Mercphobia transformed into a peaceful dragon advocating human coexistence. He saved Karameel from a shipwreck and became a benevolent ruler, caring for the citizens of Ermina. Despite his protest, Y/N allowed Mercphobia to live peacefully among the humans alive due to their friendship with each other. 

(human form) 

(dragon form) 

4. Selene A.K.A. the Moon Dragon God. Her powers revolve around the stars, the moon, and the power of transportation between worlds, being monikered as the "Dragon that crosses dimensions". Wanting to destroy the other Dragon Gods before they came to kill her, she sought and forced the priestess Faris into an ultimatum: to either destroy the other gods and to reduce of Magic Power in Earthland, or the acquisition of Elentear for her own; a different dimension where magic power is overabundant in comparison to Earthland and Edolas. She is noted for her ambition to eliminate her counterparts. Selene leads the Moonlight Divinities and presides as the Guild Master of Diabolos. 

(human form) 

(dragon form) 

5. Aldoron A.K.A. the Wood Dragon God. The largest of Dragon Gods who "commands life", possessing the ability to read the minds of othersand absorb the nutrients from the living. His size is unrivaled to the point that the largest city of Guiltina rests in the palms of his hands. His powers are connected to five orbs that are represented by five guardian deities known as God Seeds that act as protection to Aldoron once awaken, given he was healing from a battle with Acnologia that spawned centuries ago.

(human form) 

(dragon form) 

That's the first half done, now onto the second which includes Dogramag and Viernes. 

The other three are OC Dragon Gods, one is the daughter of Grandeeney, the other is the son of Elexion, and the last an Ice Dragon God who happens to be in the same Remnant as Y/N and is he's from the Schnee family. 

If you have some ideas for those three Dragon God OCs, let me know at the comments below, peace out and enjoy!