Control.Applicative.WrappedMonad allows one to use the Functor and Applicative interfaces of something that is only known to be a Monad but, oddly enough, it hides its Monad interface. The proposal is to add the missing Monad instance.
A typical use case for this instance would be:
f :: Failure String m => T1 -> m T2
f = unwrapMonad . f'
f' x = do ... -- one can also use (<$>), (<*>), etc here
(NB. the Failure class is a subclass of Monad only).
A related proposal for the transformers package would be to add a MonadTrans instance for WrappedMonad as well.