No shaders will be able to render the Aether dimension and most of them won't make the Cockatrice glow properly:
It's not clear to me where our skybox rendering code is in error here, and appears to be an issue caused by Optifine's shader system. I'm not particularly inclined to patch our code for Optifine due to the project being closed-source and difficult to debug.
However, we will add an option to disable the Aether's skybox as a configuration option for Optifine shader users. While it's not the most incredible solution, it is a viable workaround for users.
We've added a config option with commit 8cb78e4bfc to disable the skybox.
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