A player in my group wants to play an Aarakocra Ranger/Warlock(I know, weird build, but he's adamant on seeing it through) of the Raven Queen, but didn't really feel like any of the Pact Boons fit what he wanted, so I took it upon myself to delve into what might fit better. I came up with the idea of a Pact Boon that allows the Warlock to enter a transformed state(hereafter referred to as an 'Eldritch Form') that reflects the nature and aesthetic of their Patron, granting them mildly increased capabilities as a Warlock, as well as a host of new Invocations specifically geared towards improving, personalising, and specialising the Eldritch Form to better suit the Warlock. I felt this fit because, already being an Aarakocra, his Eldritch Form would cause his bird-like body to become significantly more raven-like and seeping with necrotic energy. He seems to like most of what I've come up with thus far, but I felt like posting this here so I could get insight from people who know far more about homebrewing and balance than I do.

Feel free to point out balance concerns or flavor issues as well as suggestions for tweaking or clarifying certain abilities or Invocations, or entirely new Invocation suggestions if something occurs to you. Please do be gentle as I'm fairly new at this! :)

Warlock Pact Boon: Pact of the Flesh

Your patron has granted you the ability to transform your flesh into a form more fitting for one bound to their service. As an action, you may magically enter an Eldritch Form, drastically altering your appearance in a way that reflects your patron in some way, as well as gaining a number of new abilities depending on the patron. This transformation lasts for 1 minute or until you are rendered unconscious, or until you transform back as an action. You may enter your Eldritch Form up to 2 times per long rest.

When in your Eldritch form, you gain the following benefits:

- Your limbs become capable of delivering more powerful blows. Unarmed attacks deal 1d6 bludgeoning damage instead of 1 and you become proficient in unarmed attacks.

- Your Eldritch Form renders your mind and will more resistant to assaults due to the connection to your patron. When you enter your Eldritch Form, you gain advantage on Wisdom or Charisma saving throws until the Form ends.

- Your Eldritch Form counts as your spellcasting focus for the purposes of supplying material components for spells as long as the components are not consumed or do not have a gold cost listed in the materials.

Pact of the Flesh Eldritch Invocations

Otherworldly Resistance

Your Patron grants you resistance to a damage type with which it has some type of affinity. When you gain Otherworldly Resistance, choose one of the damage types listed below with your Patron. You gain resistance to that type of damage whenever you are in your Eldritch Form. You may take this Invocation up to two times.

Resist Acid: Undying, Seeker
Resist Cold: Lurker in the Deep, Raven Queen
Resist Fire: Fiend, Celestial
Resist Lightning: Lurker in the Deep, Archfey
Resist Necrotic: Undying, Raven Queen
Resist Psychic: Great Old One, Seeker
Resist Poison: Fiend, Hexblade
Resist Radiant: Celestial, Archfey
Resist Thunder: Hexblade, Great Old One

Patron’s Resilience

Your Eldritch form radiates a minute amount of protective magic. When in your Eldritch Form, you gain a 2 bonus to AC.

Gift of Flight (req. Raven Queen, Celestial, Fiend, or Archfey Patron)

Your Eldritch Form grows a pair of wings that match its current form, or improves whatever method of flight you already have. When in your Eldritch Form, you gain a flying speed equal to your walking speed. If you already have a flying speed or if you gain a flying speed through other means, your flying speed becomes one of those amounts 10ft, your choice.

Elemental Blast

Your more intimate connection to your patron’s power allows you to force the nature of your Eldritch Blast spell to change. Whenever you cast Eldritch Blast, you may have it deal another damage type instead of force damage based on your patron, as referenced in the table below.

Cold: Lurker in the Deep

Fire: Fiend

Lightning: Archfey

Necrotic: Raven Queen, Undying

Psychic: Great Old One, Seeker

Radiant: Celestial

Thunder: Hexblade

Eldritch Talons

Your Eldritch Form’s limbs become further empowered, growing claws or talons from them and becoming swift enough to make repeated strikes. While in your Eldritch Form, your unarmed attacks now deal 1d8 bludgeoning or slashing damage (your choice) plus an additional amount of force damage equal to your proficiency bonus. Your unarmed attacks count as magical for the purpose of overcoming resistance and immunity to nonmagical attacks and damage. If you make an unarmed attack as part of the Attack action on your turn, you may make an additional attack as a bonus action.

Eldritch Recovery

When you enter your Eldritch Form, a burst of magical energy saturates your body that you may choose to harness as a means to regain spent power. Whenever you enter your Eldritch Form, you may choose to recover one Warlock spell slot. Once you use this ability, you may not do so again until you finish a short or long rest.

Form Fluidity (req. Level 10)

Your familiarity with your transformation allows you to both undergo it quicker and maintain it for longer. You may now use your Eldritch Form as a bonus action, the transformation now lasts for up to 1 hour or until you dismiss it as a bonus action, and you may use your Eldritch Form up to 4 times per long rest.

Foul Immortality (req. Undying patron)

Your patron’s immortal nature fills your Eldritch Form, allowing it to remain standing after sustaining normally lethal blows. If damage taken would take you down to 0 hit points, you must make a Constitution saving throw (DC 5 damage taken). On a success, you drop to 1 hit point instead. The DC of this saving throw increases by 2 every time the ability triggers, resetting on a long rest. This ability cannot be used if part of the damage that reduces you to 0 hit points is from radiant damage or a critical hit.

Eyes of the Undeceived (req. Seeker or Great Old One patron)

Your patron’s vision allows you to see things normally imperceptible, and things that would drive mortal minds mad. When in your Eldritch Form, you see invisible creatures and objects as if they were visible, and you can see into the Ethereal Plane. Ethereal creatures and objects appear ghostly and translucent.

Elder Power (req. Level 7)

Your closer connection with your patron allows you easier access to some of their power. When in your Eldritch Form, you may cast the Level 1 spells on your Patron’s spell list at-will and without expending any material components or spells slots. You cast these spells at their lowest level and you cannot cast them at any higher level by using this ability. You may re-take this Invocation once you are at least Level 13 to gain the same benefits for your Patron’s Level 2 spells.

Hexed Claws (req. Hexblade patron)

Your patron’s affinity for weaponry and martial prowess extends to your Eldritch Form and is reflected as such. The Hexblade’s Hex Warrior ability applies to your unarmed attacks whenever you are in your Eldritch Form.

Grasp of the Deep (req. Lurker in the Deep or Great Old One patron)

A pair of tendrils conceal themselves in your forearms whenever you enter your Eldritch Form. As an action on your turn, you may have the tendrils lash out and attempt to grapple one creature within 10ft. that is Large or smaller. Make a spell attack against the target. On a hit, they take 2d4 your Charisma modifier bludgeoning damage and are grappled (escape DC equal to your Warlock spell save DC). As an action, you may attempt to throw a target grappled by this feature. Make a spell ability check contested against their Strength. On a success, you throw the target 30ft in any direction and they take 3d6 bludgeoning damage and are prone. On a failure, they break free of the grapple. Alternatively, you can use your action to tighten your grasp on them, dealing another 2d4 Charisma modifier bludgeoning damage to them.

Eldritch Disruption (req. Level 5)

Your patron has granted you knowledge to protect yourself against magical assault. You can cast Counterspell or Dispel Magic once without consuming a Warlock spell slot. Once you cast either spell this way, you may not do so again until you finish a long rest.

Force of Will

You have learned to channel your spellcasting ability into your physical prowess. While you are in your Eldritch Form, you may use your Charisma bonus as opposed to your Strength bonus for a single Athletics or Acrobatics check. You may use this ability three times per long rest.

Eldritch Rebirth (req Level 15)

Your patron has decided that you are too valuable an asset to let die easily. When you die, your body disappears from that plane of existence and reappears in the Ethereal plane. At the end of your next turn, you reappear on the plane you left in an unoccupied space within 60 feet from where you vanished. You regain a number of hit points equal to twice your level and are in your Eldritch Form. Once you use this ability, you may not do so again for two weeks.