when i play the mod with oculus (port of iris) i get an error which says that the iris's shadow distance option cant inherit from a final class OptionInstance:

java.lang.IncompatibleClassChangeError: class net.coderbot.iris.gui.option.ShadowDistanceOption cannot inherit from final class net.minecraft.client.OptionInstance

when i use each of the mods alone there are no problems

Please post the full crash log when filling in an issue, not just the bits that you think are relevant.

From what you posted I don't see how this could be a problem on my side of the fence but let's see the whole log