@paatz04 The blue rim light is implemented as follows:
1) 2D Light Blend Style layers are setup in Example 2D URP Renderer Data.
Rim is assigned at the red (R) channel of masks.

2) There is a global Rim Light gameObject with a 2DLight component of blue color, with Blend Style set to Rim (like a layer just an integer set to 1).

3) The skeleton's material now has a Mask Texture assigned, where the mask's red channel determines how much any 2DLight with Blend Mode Rim is to be applied. In this case, stretchyman-rim-mask is set to white only near the outer edge, where the rim light should be applied. Actually it would work the same with only the R channel being set. The G and B channels of the mask texture have no effect since no 2DLight uses Blend Mode using the G or B channels (and the Example 2D URP Renderer Data does not define anything for G and B channels).