Vishanti is actually three entities in one body, or three separate entities that are all the same. It's kind of confusing, but that's what you get when you're dealing with all powerful beings. They don't play by our rules. Vishanti consists of Oshtur, a woman, Hoggoth, a tiger, and a sorcerer named Agamotto. Together, they are incredibly powerful, though not completely immortal. In fact, they've had to request help from someone familiar.
At one point Vishanti had to face a similar trinity named the Trinity of Ashes. Vishanti didn't' want to take any chances so they asked Doctor Strange for help. Doctor Strange said, "sure. Why not? Is this a weekend thing?" Then they told him the war might last a millenia so he dipped out. A millennia is a long time to commit to something. I can't even commit to finishing this article.