Elder God vs. Phantoon
Nosgoth was burning. It did not trouble the god. More souls, free of their mortal prisons, would be returned to him. The Wheel would turn, and the god would feed. So it would always be. Soon the plague would be dealt with, the vampire scourge wiped from the land like so many scattered leaves, and their dry and shriveled souls would again be his, to turn once again to Fate. But they were not.
They should have been his. What manner of creature was this, that scoured the world as if cursed with the same horrible hunger? Was it flesh or spirit, a thing not known to even immortal minds? It was the cause of this purge, a second parasite nurtured in the torturous womb of this shattered world. Prophecies failed before it, and how could they not? The form of this creature was simply alien, but not unlike the god's own. Tentacles adorned it, and its burning eye mirrored the god.
"Foolish beast," the god told it. "Your hunger is mine, and I know your mind. You cannot stop the Wheel of Fate."
There was no response but a screech of rage. It did not matter. The god could afford to be patient now, and forever. Time mattered little.
The beast began to feed. Souls flocked to it, transformed by its rage. Prisons formed again, macabre displays of bone and spirit, crying out in anguish and despair that would have been pleasing but a moment before. And the Wheel began to slow.
"No!" The god cried at this new scourge, this new plague. The souls could not return, trapped as they were by this alien beast. The god took action for the first time in centuries, raising his limbs in challenge. "You will feed the Wheel."
Now the beast turned, and its eye beheld the god. It bellowed in rage once more, and began the assault.
/fanfic
Phantoon, the multidimensional ghost of a Cosmic Horror takes the fight to Nosgoth, facing down the Elder God, the multidimensional Terrestrial Horror.
Just to make it perfectly clear, both combatants can see and harm one another. The battle takes place in a massive cave large enough to contain Phantoon and a reasonable portion of the Elder God. Phantoon's goal is to kill or otherwise get past the Elder God before going off to raze the rest of Nosgoth. The Elder God's goal is to kill or drive off Phantoon to protect the Wheel of Fate.