CompChangeWeather is a simple comp class that makes the animal change the map's weather as soon as it spawns. This class is only recommended for animals that spawn as part of an incident or quest

    //A comp class that makes this creature change the map's weather when it spawns (Fog by default)

    public string weatherDef = "Fog";

It is a comp class, so you just add it in XML in the <comps> tag. For example, this allows Foglers in RimWorld - Witcher Monster Hunt to change the map's weather to fog as soon as they spawn in the map

<comps>
	<li Class="AnimalBehaviours.CompProperties_ChangeWeather">
		<weatherDef>Fog</weatherDef>
				
	</li>
</comps>