Egypt and its mythos is often seen revolving around a great deal of respect being placed in its gods and goddesses. Many pyramids acted as valiant and glorious tombs for significant figures in the Egyptian world to rest, but also to pay respects and grace to the all-mighty gods which the Egyptians respected. In many mythological stories, followers of a faith might fear their gods and obey them out of a fear of divine punishment. The Egyptians often shied away from this sort of following, and instead chose to dedicate themselves to their gods out of respect and trust.
Very few in Egypt did not respect and trust these gods. Those who didn't would often be seen as insignificant enough to hardly matter at all to the majority of the population. However, there was one woman who not only grew to instill fear into Egyptian civilians, but the gods themselves. Vala originally did not despise the gods, but simply couldn't care less about the mythos or any sort of higher power. She would raid tombs and ransack shrines, tearing down any mediums between Egyptian faithfuls and the gods themselves. Soon, however, she began to grow a deep and much more severe hatred for the gods of Egypt. They attempted to stop her by any means necessary.
Vala suffered death again and again, but managed to cling onto her otherwise meaningless life by a thread every time. As if for no reason other than defying the rule of the gods, Vala continued her pillaging and became increasingly violent. Her violence was never directed towards Egyptian citizens themselves, which may be why despite their fear, they never rose against her.
Vala's actions slowly disconnected the Egyptian faithfuls from their gods, and relations within the religion began to wear down. The gods became weaker as a result of receiving less prayer and losing much of their hard-earned faith. Vala became known as the sole person capable of not only defying the gods, but also toppling their supreme rule.
Vala mortified the gods, and began to to rob them of sacred artifacts and powers which had been sealed deep within their tombs. Secrets of creation were revealed to the citizens of Egypt through Vala's actions, and uprisings began against the gods. Upon the night of October 31st, Vala finalized her spiteful strive to muddy the reputation of the gods. Throughout the night, she strove to horrify the citizens of Egypt however possible. Assembling the mummified remains of past leaders into scarecrow-like figures strung to crosses throughout the villages; ransacking the farms and crops, lighting them on fire and ruining the already dwindling food supply; the fire around the crops seemed almost sinister to the Egyptians, as if the melons and pumpkins were smiling back at them with grins as evil as Vala herself. As the power of the gods dwindled due to a lack of faith, Vala was able to harvest more and more of that power through the artifacts which she had stolen. Using her new-found power, she granted every entity in the underworld a right of passage to the overworld once more, on one condition. No ghosts, demons, ghouls, or monsters would be permitted to attack the Egyptian people. For one night every year, they could stretch their legs and roam the country free of their endless torture of the underworld. That night would be known as Halloween.
It was uncertain why Vala had gone to the extremes that she had on that night. Many believe that her human mind and body could not grasp the power which she had accumulated over many priceless artifacts and items imbued with the magic of the gods. Others think that Vala had set out from the beginning to end the rule of the gods. The scariest part about Vala was the mystery behind her actions.
All human fears are variations on the fear of the unknown. Vala embodied that fear. Although not sinister in herself, the people of Egypt didn't know whether to fear her, praise her, or simply treat her as a peer.
My storytelling is a bit weak, I apologize. 
Heimdallr's ultimate.
Honestly I think your storytelling is just fine. I at first thought the story was weak, as it's a very limited writeup at the top. Had to get past the abilities and pics to find the true writeup, which I think is quite unique and interesting.
I find things that I'd consider to be major flaws in the concept. She has absolutely 0 direct ability damage, and outside of her ult, 0 CC of any type. The first ability is just vision and passive MS. The second is damage reflect. The third is basically a stance shift from melee to ranged. And the ult also doesn't deal damage, just takes her and her target to a different area. That's a huge oversight, as every god should have some form of damage in at least 1 ability. How the heck is she clearing minions outside of
With no dash or other mobility outside of her ult, she relies on the somewhat increased MS from the 1 to close on an enemy. But she has no CC immunity, so slows (which are often more powerful than the MS boost she'll get in her 1) can shut her down outside of ranged basics. And there should be some bonus to being in the more difficult melee stance vs ranged. And as an Assassin, how would
The 2 does have the ability to be quite OP, but very, very situationally. Outside of a quick reaction to counter something like Poseidon's or Scylla's ult, the 1.5 seconds of invulnerability-to-reflect damage should be easily avoided similarly to spotting the activation of
I think there's a missed opportunity in your lore. "Using her new-found power, she granted every entity in the underworld a right (rite) of passage to the overworld once more, on one condition. No ghosts, demons, ghouls, or monsters would be permitted to attack the Egyptian people. For one night every year, they could stretch their legs and roam the country free of their endless torture of the underworld." One of her abilities could bring some minions to help her do damage, provide some CC, something to help out the lack of stuff in the rest of her kit.
Anyway, I see a lot of potential in a concept like this, but the abilities would need some significant revamping.