That’s the thing where they have flames all around them, right?
I guess draw yourself the basic shape of what you want. Spiky on the outside, fuzzy on the inside. Do this in photoshop and import it, or create a solid layer and put two masks on it. The outer mask is an Add mask, the inner mask is Subtract, and should have a very high feather value, like 50 at least. Pre-comp the layer and apply a Turbulent displace. Animate the Evolution property of the displace.
Make another layer; Apply the fractal noise effect and colorama or tint to make it the colour you want your flames. Put the layer in add or lighten mode. Animate the “offset turbulence” property of the fractal noise so that it’s moving up.
Use your first layer as a track matte for the second layer.