To make the character more visible, we sample the depth buffer and fade the shield as a function of the distance to the shell.
So the nearby areas (likely the character) become more transparent, while the farther areas (which are probably the background) get the full effect.
The shield here is the enlarged mesh.
The shell means the original model (I assume).
I am well familiar with sampling the depth buffer, but how would I calculate the distance to the shell from my current pixel based on the value from the depth buffer? there is no way (I can think of) to know if the depth value comes from the original model or from another player, a wall, etc. ?