"Assets\Campfire_burning.et" very strange path, first once - slash is wrong, second one - prefab is Assets folder.
All prefabs in "Prefabs" folder.
Try this "{899360C930DA3EE3}Prefabs/Particles/Campfire_burning.et"
On future: right mouse click -> "Copy resource name(s)" on prefab to get path to it
Check logs and use checks in code:
Resource resource = Resource.Load(prefabResourceName);
if (!resource.IsValid())
{
Print("Cant load prefab");
return;
}
And very strange design to use "modded" class. Create own component and attach it to GameMode or player.