Titan is already represented in the game as cold toxic, I presume... I guess methane is a planet like Titan, minus the extremely dense atmosphere caused by volcanic activity. So, it's just average atmosphere density retaining a strong greenhouse effect, with low temperatures allowing for the existence of all three states of methane. Kinda like water does in our temperatures.
Okay, solved.
darn, wished the person behind the mod still worked on it. Would be cool if they added hycean, carbon, diamond or fire giant worlds. And I was also having dreams where I saw singularity giants... Strange glowing purple gas giants that contained arcane black hole energy. In case it came to something more fantastical. They had like a 50% habitability penalty of like a horrifying status effect. I also remember there being disjointed black hole parts patrolling a system... Man that would be flipping scary if it was real.