Resolved Unity Gem shader and LWRP

If you follow these steps you can get the gem shader to work properly with Universal RP or LWRP:

1. Add

Tags{"LightMode" = "PassTwoPostTransparent"}

to the beginning of the second pass of the shader.

2. Replace the shadowcaster usepass near the end of the shader with

UsePass "Universal Render Pipeline/Lit/ShadowCaster"

in order to make shadow casting work properly. If you're still using lightweight (2019.2) use this:

UsePass "Lightweight Render Pipeline/Lit/ShadowCaster"

3. Select the forward renderer for your Universal Pipeline Asset and create a Renderer Feature, add the shader pass with the same name and make sure "Layer Mask" is set to whatever layer your gems are on, Event is set to "After Rendering Transparents," and that a Shader Pass filter is added with the name of the pass.
Note: the renderer feature name can be whatever you want, but the Shader Pass name must match the lightmode tag that you put in the pass.

If you're using LWRP (2019.2) make sure to create a custom LWRP forward renderer (Create -> Rendering -> Lightweight Render Pipeline -> Forward Renderer) and set your Lightweight Render Pipeline Asset's Renderer Type to "Custom" and make it use your custom forward renderer.

I hope that helps!