Within your soul is a spark of power that the universe recognizes.  A past life, or even an alternate self, touched on an aspect of creation or the divine and imbued power into you; seeking an outlet, your current incarnation was offered a chance to bring out that power, and you took it.  Now, your past and alternate selves empower your current incarnation directly.

Vestige Focus

Starting at first level, you tap into an aspect of your vestige to grant you power, changing the aspect as needed to give you an advantage from your past and alternate lives.  After a short or long rest, choose a focus from the following list.  Each focus gives you an individual, passive power.  You may change your focus as a bonus action, once per short rest.  Alternatively, you may change your focus when you use a warlock spell slot.

Protective Vestige

Channeling the aspects of your soul that focused on protection and safety, you gain a +1 bonus to your armor class.  At level 11, this bonus becomes +2.

Soul Strikes

You learn to channel the power of your soul into a pact weapon or into your fists.  Your pact weapon attacks or your unarmed strikes are treated as magical.  At level 11, the damage type is replaced by psychic for your pact weapons or unarmed strikes.

Vestigial Knowledge

You gain proficiency in one intelligence, wisdom, or charisma  skill you are not proficient with.  You also gain proficiency in either a tool or a language of your choice.  At level 11, you may choose 2 skills and 2 tools/languages.

Thoughts as Words

Starting at first level, a vestige warlock has a minor ability to project mental messages.  You gain the Message cantrip, but it requires no components (verbal, somatic, material) and has no visible sing of effect.  If the target is unwilling, the power fails.  If the creature cannot speak a language, any response is in emotions.

Channel Vestige

At 6th level, the warlock can manifest one of his vestiges, and the two work in tandem to increase the warlock's power.  While this ability is active, the warlock is under the effect of a Haste spell that does not require concentration.  In addition, he has advantage on all dexterity, intelligence, and wisdom ability checks.  This power lasts for 1 minute, and cannot be used again until the warlock takes a long rest.

Mind of the Vestige

Starting at 10th level, your thoughts cannot be read by telepathy or other means unless you allow it.  Against any spells or abilities that would affect your mind or soul (such as feeblemind or Imprisonment, as well as charm spells), you have advantage on any saving through.  Additionally, you are resistant to psychic damage.

Act as One

At 14th level, you and your vestiges act as one.  You may take up to 3 actions this turn.  This causes incredible strain and the warlock gains a level in exhaustion; this exhaustion does not affect the warlock for 1 minute.  This ability may be used once per long rest.