options is a special property that unlike other objects that you pass to extend will be merged with the parent one instead of overriding it completely, which makes managing configuration of objects and default values convenient.
statics is just a convenience property that injects specified object properties as the static properties of the class, useful for defining constants.
includes is a special class property that merges all specified objects into the class (such objects are called mixins). A good example of this is L.Mixin.Events that event-related methods like on, off and fire to the class.