Tiamat

General abilities: can produce electricity from her body, transformation (only to dragon form and vice versa), longevity, superior healing (takes a shorter amount of time for injuries to heal compared to humans), ability to store electricity and increased senses (smell, sight etc.)

Dragon form abilities: Tiamat retains the same abilities from her other form as well as - lightning "breath", levitation, flight, further improved senses, more powerful healing abilities (able to heal from life threatening wounds in the right circumstances) 

Deity form abilities: retains all other abilities from other forms, dimensional travel, reincarnation, able to control the weather, powerful enough to destroy entire planets via weather anomalies (storms etc.)

Reincarnation: this ability allows her to be "reborn" when ever she dies, sometimes being reborn in completely different universes. She is always reborn looking the same. Her knowledge of previous lives does not carry over but sometimes particularly powerful memories will trouble her in her sleep. She could be considered a true immortal.

Dragon form: In her dragon form her personality changes as her draconian powers surge. She is far more aggressive, angry and unattached; things that normally she would never consider due to her moral code are now clear options to her. This form is a halfway point between her "normal" form and her true identity which is why there is such a change in her personality; her true personality starts to bleed through. Her humanoid form acts as a limiter on her draconian powers which is why she is stronger in her dragon form.

Deity form: Tiamat is the dormant form of a deity of destruction and rebirth know by many names such as the Infinite One, the Eternal Chain, the Ouroboros etc. A dragon-like being that represents destruction and rebirth. Her purpose is to destroy any universe that has reached it's "end" so that a new one may take it's place. Tiamat is unable to control this and is compelled to fulfil her role. Her real personality is cold and lonely, unable to form attachments due to her position since she will either outlive or destroy anyone who comes into contact with her. Even among the other deities she is alone, none will ever live as long as she will; she will last to the end of all times only for it all to begin anew, the cycle continuing forever. 

Other info:

• In her dragon form, Tiamat can produce more than 6000 volts. This electrical power is stored in her horns on her head, neck and back and cause them to glow. This electricity is caused by the friction of her hair along her back and the horns have a natural ability to draw in electricity. They are essentially lightning rods.
• When Tiamat (in human form) becomes angry her horns will start to glow.
• It could be argued that Tiamat and Ouroboros are two separate beings due to their radical personality differences or even that Tiamat does not truly exist. Ouroboros supresses her memories as a god while in her humanoid form as a way of trying to experience life as a human due to her loneliness.