Fancy Rain breaks a few mods
PickleTweaks and TwilightForest are not compatible with the fancy weather.
Not compatible how? I have Twilight Forest, and haven't noticed any problems yet.
It also doesn't work with Dynamic Surroundings' Nether weather. You can see the smoke, and it's all fancy, but the actual embers are missing. It could work by spawning them from Netherrack and having them blow around randomly, maybe turning in to smoke when they hit something rather than it being on top of every block. It would probably even look better than the normal one, since it won't be inside buildings built with non-Nether materials.
If any of the mods didn't like that I prevented rain particles from spawning, then it won't cause problems anymore.