You have a class X, you have a class called XHelper. XHelper contains methods that make it easy to use X.
The problem I have with this antipattern is that XHelper does nothing of value. If the methods are truly related to X then they should actual be class methods of X. However if you need “helper” methods to use the API of X chances are what is really required is a refactoring of X to incorporate the enhancements of XHelper invisibly. You shouldn’t need a helper to use an API.
Take Rails page helpers. A helper to construct the content of a page contains functionality that would be better marshalled in the controller, prior to view rendering. If multiple controllers perform the action then extract it to a service that controllers can invoke on the requests and delegates they are co-ordinating.
What if the Helper class actually refactors common functionality from classes X and Y and is actually called FooHelper because it helps perform Foo in X and Y?
Well, here we are onto something, we have some common functionality which is good and the name of the class reflects its purpose. The same question arises though, could FooHelper’s methods actually reside in Foo? If Foo is purely a function or method call then perhaps all the functionality relating to Foo should be encapsulated in a Foo class that presents the foo method.
Alternatively perhaps there is a better name than “Helper”? As examples, I tend to call collections of class methods that transform instances of one class into instances of another class “Transformers”. Similarly methods that create database connection instances could be called “Providers”. If you cannot make the class a private class instance of the class or classes the Helper is nominally a Helper to, then there is usually a better name for the class lurking around somewhere.