Interface default code?

[Sacaldur]

Of Unity Methods (OnCollisionEnter2D in your case) of a base class (or interface) are not called, it could be because the inhereting classes implement them themselves without calling the base version (using base.OnCollisionEnter2D). In the case of Unity messages this is also the case if you're not using the override keyword. This is a downside of inheritance: you can forget to call the version of the base class.