If you were to add/make a new Pokemon what would it look like and what would his name be

So there is a creature. I don't know if it actually exists, but it's a snake that bites its tail and rolls around in a hoop shape. That's how it travels. However, it has the deadliest poison. So if you were to encounter one, you're practically dead because it rolls fast and one bite kills you.

I'd want it to be based on that. There would be an evolution chain. The first one is just poison. Its poison is still developing, so it's not deadly and still learning to roll so it sometimes flops around and falls over. It would be just white with red eyes. Its shiny would be pure black with green eyes. It evolves when it manages to roll consistently. (In the video game you just walk with it for a little bit (not like those 2500 steps. It wouldn't be much) and reach level 15)

The next evolution would now be able to roll, and its poison has more power. It's longer and thicker than the basic, and it's still white, but small purple-ish/black dots begin to form om it's body (black with silver-ish/white). It is still only poison. It evolves when it knock out 25 opponents. (Both game and anime)

Its final evolution would have the deadliest poison and quickly switches between slithering and rolling, making it nearly impossible to hit or catch. Its dots on its scales have taken the form of skull, signaling to enemies its deadliness (the shiny and normal color palettes are the same still). It is now part Ghost type, showing how connected to death it is. It would have a move unique to it, but I don't know what. Its ability is the one that let's it poison Poison types.