The trick is that it is not a monoid AND and endofunctor but of monoid OF endofunctors. The whole "monads are monoids in the category of endofunctors" was a jok

The trick is that it is not a monoid AND and endofunctor but of monoid OF endofunctors. The whole "monads are monoids in the category of endofunctors" was a joke because it is a needlessly complex way of describing what a monad is.