Invoke a function if it has a defined Decorator Pattern

I don't know if I'm using the wrong pattern or what. I'm have a standard class and 3 decorators:

MyClass, Dec1, Dec2, Dec3.

everyone implements MyClassInterface { getDescription(), addDescription(String t) }. But Dec2 has also the function { specialFunction() }.

I create an instance:

MyClassInterface instance = new Dec1(new Dec2(new Dec3(new MyClass())));

then I would call the specialFunction, but I can't! If I would have done this with Dec1 that extends Dec2, that extends Dec3, that extends MyClass, would have been possible.

It would be nice having a function like

decoratorInstance = instance.hasDecorator(Dec2)
decoratorInstance.specialFunction()

But I don't know if it is possible without making a huge pattern mistake.