Feats

Favored of the Archfey

One of the Archfey has granted you great favor. Increase your Charisma score by 1, to a maximum of 20, and gain the appropriate feature below.

• The Seelie Queen:
• The Green Man:
• The Silver Knight: As a bonus action, teleport to a space within 60 feet. Your destination space must be threatened by more creatures than the space you are leaving. Once you do so, you must complete a short or long rest before using this feature again. 
• The Muse of Steel: You can use any type of artisan's tools as a spellcasting implement when you cast spells that you know. You learn the mending cantrip and the spells identify and magic weapon. You can cast identify or magic weapon once without expending a spell slot, and you must finish a long rest before you can cast either of those spells in this way again. You can also cast these spells using any spell slots that you have.
• The Good Fellow: When you would roll a Dexterity check for initiative, you can instead choose to roll Charisma (Deception) for initiative.
• When a melee attack misses you, you can spend your reaction to teleport to an empty space on the other side of the opponent who made the attack, and you can make one weapon attack. Once you do so, you may not use this feature again until you complete a short or long rest. 
• The Queen of Air and Darkness:
• The Lord of the Hunt:
• The Thornweaver: 
• The Winter Lord:
• The Night Collector:
• The Mother of Redcaps:
• The Sea Hag:
• The Dream-Tyrant:
• The Eldest: 

Martial Adept (Alternate)

Add the following bullet point:

• In addition to the maneuvers available to the Battle Master archetype, you may choose one of the following options. You may unlearn one of the maneuvers on this list to learn another maneuver on this list when you gain a level. You may never learn more than one of the maneuvers of this list.
• Battaglia: When you hit a creature you can see with a dagger, you can spend one superiority die to add it to your damage roll. In addition, any die in this damage roll that results in its maximum value is rolled again, adding the result to the final damage dealt. A die rerolled through this feature that results in its maximum value cannot be rerolled again.
• Coudray: To use this maneuver, you must be wielding a shield. As a bonus action, spend and roll a superiority die. Until the beginning of your next turn, reduce the damage from all weapon attacks against you by the amount rolled.
• Kinsale: To use this maneuver, you must be wearing a cloak and one empty hand. When you are hit by a melee weapon attack, spend a superiority die and add its result to your Armor Class. If this causes the attack to miss, the target must make a Strength saving throw. On a failed saving throw, the weapon used to attack you drops at the creature’s feet.
• Moriscato: To use this maneuver, you must wield two weapons, one of which is a dagger. When you attack with your dagger and have advantage, you may spend a superiority die to roll two dice of the same type and add them to your damage roll.
• Roux: When you roll a Dexterity or Intelligence saving throw, you may expend one superiority die to add it to that roll. When an ally adjacent to you rolls a Dexterity or Intelligence saving throw, you may expend a superiority die and add half its result to the roll.
• Rowan: When you roll a Strength or Constitution saving throw, you may expend one superiority die to add it to that roll. If you fail the roll anyway, you may take damage equal to the superiority die result to succeed instead. This damage may not be reduced or avoided, and goes to current hit points rather than temporary hit points.
• Displaced Hand/Vachir: When you roll initiative, you may spend a superiority die to attack with a ranged or thrown weapon. If this attack roll hits, the target takes damage equal to the amount rolled on the superiority die plus any bonuses from magical effects on the weapon.
• Dane's Bulwark: To use this maneuver, you must be wielding a shield. When an effect would knock you prone or force you to move through any means other than teleportation, you may spend a superiority die. Add the result to any saving throw or ability check to resist this movement. If you fail the saving throw or ability check, you may spend your reaction to take damage equal to the superiority die result. If you do, you are not moved or knocked prone. This damage may not be reduced or avoided, and goes to current hit points rather than temporary hit points.

• Lost Blades of Mazhan: When you attack with an off-hand weapon as a bonus action, you may spend one superiority die. Roll one die of that type for each attack roll you have missed in this turn and add the result to the damage roll of your off-hand attack. 

• Sand Spire: To use this maneuver, you must be wielding a spear, glaive, halberd, or pike. When an enemy you can see within your reach makes a weapon attack against one of your allies, you may spend a superiority die to make an opportunity attack against that enemy, adding the superiority die result to your damage roll.

• Shieldeaters: When you roll initiative and you are not wearing armor or wielding a shield, you may choose to expend a superiority die. For the duration of that encounter, your Armor Class is the die's result + your Dexterity modifier.

• Silver Swordsmen: To use this maneuver, you must be wielding a silver, or silvered, weapon. When you are the target of an effect that deals necrotic damage, spend and roll a superiority die to add its result to your Armor Class (if this is a weapon or spell attack), or your next saving throw (if a saving throw is necessary). 
• Iron Temple:  When you roll a Wisdom or Charisma saving throw, you may expend one superiority die to add it to the roll. When an ally within 30 feet rolls a Wisdom or Charisma saving throw, you may use your reaction to expend a superiority die and add half its result to the roll.
• Sovereign Knights of the Council Fire:  When an ally adjacent to you takes damage from a weapon or an effect that allows a Dexterity saving throw, you may expend a superiority die to reduce the damage taken by the die's result. If you are wielding a shield, add the higher of your Strength bonus or Dexterity bonus.
• Tiger's Claw:  When you use the Attack action to make melee attacks with a one-handed weapon, you may spend a superiority die to fire a loaded flintlock pistol as a bonus action. You may expend a number of superiority dice up to the number of your melee attacks in this turn that hit; add the value of those dice to the damage of your flintlock pistol.
• Cursewardens:  When you fail a saving throw against a spell of 1st level or higher, you may expend a superiority die to inflict that much necrotic damage to the spell's caster.

Mystic Clarity

Prerequisite: Able to cast at least one spell

Thanks to rigorous discipline in practicing magic, you gain the following benefits.

• When you cast a spell that restores hit points to an ally, you gain temporary hit points equal to the highest die value that you roll. These temporary hit points last for up to one hour.
• Gain advantage when you make a Constitution saving throw to maintain Concentration on a beneficial effect you have cast on an ally.
• When you fail a Constitution saving throw to maintain Concentration, you may choose to gain a level of exhaustion and treat the saving throw as a success instead. All exhaustion gained in this way is removed with a short rest.

Mystic Corruption

Prerequisite: Able to cast at least one spell

Thanks to ruthless dedication to the ways of magical power, no matter the costs, you gain the following benefits.

• When you roll damage for a spell you cast, you may choose to gain a level of exhaustion to reroll a number of dice equal to your proficiency bonus. You must keep the new result. All exhaustion gained in this way is removed with a short rest. 
• Gain advantage when you make a Constitution saving throw to maintain Concentration on an effect you have cast on an enemy.
• When you cast a spell of 2nd level or higher and all creatures in its area or that it targets are immune to its effects, you regain an expended spell slot. That spell slot must be of a level lower than the spell you cast. If you used Pact Magic to cast the spell, your Slot Level for that Pact Magic spell slot decreases by 1 until you complete a short or long rest.

Invocations

Blood Sacrifice

As an action, sacrifice a number of hit dice equal to the level of your Pact Magic slots to refresh a Pact Magic slot. Once you use this ability, you may not do so again until you complete a long rest (alternately: until you use the Recuperate downtime action).

Danse Macabre

As an action, you may target one undead creature you can see within 30 feet. The target must make a Wisdom saving throw against your spell DC. On a failed save, the target must obey your commands for the next 24 hours. An undead creature whose challenge rating is equal to or greater than your level is immune to this effect. Once you use this ability, you may not do so again until you complete a long rest.

Notes: Based, obviously enough, on the Oathbreaker paladin's Command Undead ability, but once per long rest rather than once per short rest, as a Channel Divinity. I've been meaning to write up the Grim Reaper as a warlock patron, and this feeds into that idea.

Eldritch Cloak

As a reaction, whenever you or someone within 5 feet of you rolls a saving throw against a magical effect, you may add 1d6 to the result. Declare this ability after the saving throw is rolled but before the DM declares the effect.

Labyrinth Walker

In some settings, this may be restricted to warlocks with Archfey patrons.

You are experienced in the mental discipline and mysteries of walking a labyrinth. You gain advantage on all saving throws against the charmed condition, the frightened condition, and the spells compulsion, confusion, and maze.

Master of Maledictions

As a bonus action, you place a curse upon a creature you can see within 90 feet. This requires your Concentration and lasts up to one hour. Until the spell ends, you deal an extra 1d6 necrotic damage to the target whenever you hit it with an attack. Also, choose one ability when you use this effect. The target has disadvantage on ability checks made with the chosen ability. This effect does not stack with hex. When you have used this effect a number of times equal to your Charisma modifier, you may not use it again until you complete a long rest. A remove curse cast on the target ends this effect early.

The Queen's Decorum

Requires Archfey Patron: Seelie Queen

When you cast a spell that imposes the charmed or frightened effect, or you use a class or subclass feature that imposes the charmed or frightened effect, and all targets succeed their saving throws, you may give the effect your Concentration. As long as you maintain your Concentration, you may use this spell or feature again until at least one creature fails its saving throw and becomes charmed or frightened. Once you use this feature, you may not do so again until you complete a long rest.

Sigil Perilous

You may spend 10 minutes to inscribe a rune of trial and peril. If you pass its tests, it strengthens you for battle yet to come; if you fail, it takes a dreadful toll. Whatever the outcome, you may not inscribe the Sigil Perilous more than once per week. Use one of the two models below, depending on what suits your campaign's style or the needs of the moment.

Riddles in the Dark. Through direct contact with your patron or one of your patron's highest-ranking servants, you must show your worthiness. The Archfey favor riddles and tests of loyalty, the Fiends favor demonstrations of the corruption deep within your soul (and tests of loyalty), and the Great Old Ones favor mind-shattering pseudo-mathematics. (I don't know how a DM might test a PC on that last one. Let's say I'm leaving that as an exercise for the reader. Ahem.) To pass, warlocks of levels 1-5 must answer at least one question correctly out of five (or whatever amounts to 20%); warlocks of levels 6-11, two or 40%; warlocks of levels 12-17, three or 60%; and warlocks of 18th level and above must answer four or 80% correctly.

Let the Dice Be Your Oracle. Your patron tests your Charisma, and one ability score appropriate to your patron's nature and your own bond with that patron. Archfey typically test Wisdom (or Insight), Fiends, Constitution; and Great Old Ones, Intelligence (or Arcana). Roll five ability checks, of increasing difficulty; the DM decides which abilities your patron tests, and these are often different from one trial to the next. The ability check DCs do not increase according to your level. To pass, warlocks of level 1-5 must succeed two checks; warlocks of level 6-11, three; warlocks of level 12-17, four; warlocks of 18th level and above must succeed all five checks to pass the test.

Success! If you succeed, you may use each feature that your patron grants you one additional time before taking the required rest. (That is, the class features specific to your Patron.) This benefit fades when you next take a long rest.

Failure... If you fail, for the next 24 hours, you make all spell attacks with disadvantage, and you grant advantage on all saving throws that you force opponents to make.

Notes: This is obviously complicated to resolve, but I liked the name The Sigil Perilous, and this is what I came up with for that to do. This invocation emphasizes the warlock's relationship with the patron, and might just as easily be part of an antagonistic relationship as a more cooperative one. It's definitely not for every group, in any case.

Tendrils of Ruination

Prerequisite: 15th level

As a bonus action or reaction instead of an action, you may cast arms of Hadar as a 1st-level spell without expending a spell slot, even if you to not know the spell. If you do know the spell and spend a warlock spell slot, you may instead cast it as any spell level up to 5th.

Weaver of Twilight

Prerequisite: 3rd level

You can cast web once using a warlock spell slot. Once you do so, you may not do so again until you complete a long rest. When you reach 9th level, this invocation no longer costs a warlock spell slot, but you still must complete a long rest in between uses.