Leviathan's Eldritch Blessing

The Leviathan has noticed you, for good or ill.  You learn one Eldritch Invocation option of your choice from a select list of Warlock invocations. Your spellcasting ability for the invocation is Intelligence, Wisdom, or Charisma (choose when you select this feat). 

Whenever you gain a level, you can replace the invocation with another one from the select list.