You have been cursed with the blood of an elder. Long ago, before time itself, there was nothing; there were monsters, and the beings that existed were bored with reality and fell asleep. In the dreams of these primordial dreams, all of creation was created; however, every once in a while, one of the beings would wake up and reality would falter as beings outside of creation filtered their way into reality. Beings such as humans revered these creatures as gods, their minds unable to comprehend the magnitude of the elders. In search of understanding the children of the Eternal Darkness, an order of religious priests managed to capture a weakened Elder and kill it, and they drank its blood, transferring the slightest amount of power into them in return for what little sanity they had left. However, as time went on, they realized that their bodies could not handle the blood and transformed into monsters.
Similar to the priests of the Elders, you too have been enhanced by the blood of the primordials. Unlike the priests, your body has an unusual affinity for elder blood, allowing your mind to remain intact. Your blood allows you to draw upon dark and enigmatic energies from an otherworldly realm, tapping into the very source and fundamental forces of the universe. Your body has been irreversibly changed as you disregard the natural rules of the universe. You have gained immeasurable potential as the limits previously in place for your mortal shell have been unchained. Like those from whom you have gained your blood, you also gain power from others worship, as your growth in power is enhanced when given worship by others. As you gain more power, your body changes to become more like those who came before you, turning you into an elder.
As your understanding of the blood and its uses grows, you acquire more abilities and unique uses for the blood. You start off with powerful telekinesis and telepathy, being able to lift large buildings and throw them at your enemies and read the minds of anyone within range of a city block. As your elder blood grows, you can do more, such as affect the world around you, change reality to how you see fit, absorb the souls of others, manipulate the biology of others, bring the dead back to life, create monsters, induce madness in others, and so much more.