Asking abt an animated effect in hollow knight game!

There are a few different approaches you could take to create something similar. 

One of the particle generator effects would likely be the most accurate (Particle Playground, CC Particle World, CC Particle Systems II), though these effects may take a little more experience to use effectively. You should be able to find several tutorials on any of the above. 

A fairly simple approach:
Create a solid. (If you want this effect to extend all the way to the edges, make the Solid dimensions about 50% larger than the composition's dimensions.)
Add Fractal Noise.
Add Polar Coordinates; set Type to "Rect to Polar" and then Interpolation to 100%. 
Within Fractal Noise, twirl open Transform and animate the Y value of Offset Turbulence. Adjust the other noise settings to taste. 

Add a Tint or Tritone effect to color as desired. Radial Blur set to Zoom would probably also be a nice touch. 
This look will have a seam, but there are additional steps that could be taken to remove that if needed. 

Let us know if you need additional help!