In my campaign, I recently introduced warlocks serving the Nightwalker, my setting's version of the Grim Reaper. The PCs have known they would eventually run into such warlocks, but this is the first time it has happened. Obviously, that meant I had to write a new Patron option for the Warlock class, and in so doing I also wrote a new Pact and three new necromantic spells. The new spells are a patch on the extremely small number of low-level necromancy spells that I could assign to the Patron. Some of what I'm doing is also an attempt to stake out a fourth gameplay style for warlocks. In the comments below, feel free to tell me whether I've succeeded. As usual, there are Design Notes after each section discussing why I made the choices that I did.
These spells are not added to the general warlock list, but come from the Death Patron. Two of the three are added to the general wizard list; the third, aura of hunger, is not intended to have any other current source.
Aura of Hunger
Casting Time: 1 action
Range: Self (30-foot radius)
Duration: Concentration, up to 1 minute
The awful hunger of the unquiet dead radiates from you in an aura with a 30-foot radius. Until the spell ends, the aura moves with you, centered on you. Each hostile creature in the aura takes an additional 2d6 necrotic damage when it suffers damage from any spell you cast, or when it suffers damage from any necrotic source. A creature cannot suffer this extra damage more than once per round.
Casting Time: 1 action
Range: 30 feet
Components: V, S, M (a live leech, which the spell consumes)
Duration: Concentration, up to 1 minute
When you cast this spell, you kill the leech that is your material component with a pulse of necrotic energy, and place its ethereal form on the flesh of an enemy. Your target rolls a Constitution saving throw. On a failure, the target suffers 1d12 necrotic damage, and has disadvantage on all Constitution saving throws until the beginning of your next turn. For the spell's duration, you can spend an action to inflict another 1d12 necrotic damage on the target and give it disadvantage on Constitution saving throws until the beginning of your next turn. On a successful saving throw, the target takes half of the initial damage, does not suffer disadvantage on Constitution saving throws, and you cannot spend an action in later rounds to cause further damage.
At Higher Levels. When you cast this spell using a spell slot of 2nd level or higher, the initial damage increases by 1d12 for every slot level above 1st.
Casting Time: 1 action
Range: 30 feet
Components: V, S
As you suffer, so shall your foe. One enemy within range must make a Constitution saving throw; on a failure it takes damage, and larger amounts of damage based on your current hit points relative to your maximum hit points. On a success, the enemy takes half damage.
Your current hit points are equal to your maximum hit points: 5d4 necrotic damage
Your current hit points are less than your maximum hit points, but more than half of your maximum hit points: 5d6 necrotic damage
Your current hit points are equal to or less than half your maximum hit points: 5d8 necrotic damage
Your current hit point total is 5 or less, regardless of your maximum hit points: 5d10 necrotic damage
At your option, after the saving throw roll but before rolling damage, you may spend a bonus action to inflict 1d8 points of damage on yourself, which you may not reduce in any way. If you do so, increase the damage dealt by one step (5d4 -> 5d6 -> 5d8 -> 5d10 -> 5d12).
At Higher Levels. When you cast this spell using a 4th-level spell slot, you may choose a second target. It takes the same effect as your primary target. When you cast this spell using a 6th-level spell slot, you may choose a third target. When you cast this spell using an 8th-level spell slot, you may choose a fourth target.
Design Notes on Spells
Aura of hunger explores what a scaled-up damage-kicker spell (that is, higher than hex) might look like. It doesn't scale by level, because it doesn't really need to - the class that can cast it only gets one spell level higher than that anyway, and that's not enough of a cost increase to justify another damage kicker die. Obviously, hex has its own scaling mechanic, but then low-level damaging spells have their own scaling mechanic without invalidating higher-level damaging spells, so maybe the same is true for this kind of thing.
Spectral leech is thematically inspired by 3.x's spirit worm spell, and mechanically by witch bolt. Witch bolt is widely regarded as underpowered and something of a trap spell, thanks to an intersection of drawbacks:
You lose the spell slot with no effect if you miss that first attack.
Concentration duration means you can't stack it with damage-kicker effects like hex that are the warlock's bread and butter.
d12 automatic damage sounds good until you look at your expected damage output from just spending those actions on cantrips - it's all right at 1st level, but falls off sharply once Agonizing Blast or scaled-up cantrips are on the table.
Since the spell doesn't carry a snare effect, the target can end the spell by making you fail a Concentration check (and therefore acts as a taunt) or by moving more than 30 feet away from you (and therefore acts as a melee detaunt). You're encouraging one of two opposite kinds of behavior from the enemy, and the enemy is at least 50% likely to choose the one you don't want.
Therefore, spectral leech has an effect on miss, albeit a reduced one - though if you've spent a high-level spell slot on this, at least you're getting the front-loaded benefit of doing so. It's still Concentration duration; I can't fix everything, but at least the spell's secondary effect may be a debuff another party member can capitalize on. I deliberately didn't make it something that spectral leech's caster can benefit from, because I want you to feel like spending your actions on dealing spectral leech damage is a reasonably good idea, instead of casting something else. I've removed the clause permitting the enemy to end the effect by fleeing, so the warlock just needs to take cover behind sturdy companions.
Mirrored wounds came from thinking about all of the wound-transferring spells that have been in necromancy at one point or another, but generally wanting to shy away from giving necromancers healing with this spell. Instead, it's a risk/reward spell - if you're low enough on hit points to get the greatest benefit from this spell, you're in bad trouble and might get aced. Its die-size scaling mechanic is something I first tried out in writing new cleric spells, but I think it might work a little better here. I'm... not completely sure about its spell-slot scaling mechanic, but I felt like adding more damage dice was tone-deaf. At its very best, it's kind of obscenely good (an average of 32.5 damage from a second-level slot), but dealing that "optimal" damage is a huge risk - it's a 50/50 chance that you'll take yourself out of the fight and start bleeding to death. It's probably a lot smarter to settle for 5d10, whichever way you get there.
Malediction Pact (Warlock)
You gain an additional Pact Magic spell slot that may only be used for the following spells: bane, hex, crown of madness, or bestow curse. This ability does not grant access to these spells in itself.
Once during the duration of any of the above spells, you may spend your reaction to inflict a 1d6 penalty to any d20 roll the target makes. Declare this ability after seeing the result of the d20 roll but before the outcome of the roll is announced.
Design Notes on the Pact
Warlocks are thematically all about curses, right? And hex, at least, is very good - but for the first 10 levels of play, it's pretty painful to spend so many of your Pact Magic slots on it. Crown of madness, on the other hand, is egregiously underpowered, even as the game really wants you to like it - so I'm willing to stretch a bit to give warlocks a little more reason to use it. (This probably still isn't enough.) Bane and bestow curse have to come from another source, such as Thief of Five Fates and Sign of Ill Omen... which benefit a lot from having their cost mitigated by coming from a Pact Magic slot that can't do anything else.
The Malediction Pact won't really be complete until it also has at least one invocation for which it is a prerequisite. I thought about splitting the d6 penalty to a d20 roll out as that effect, but decided against. I'm not sure what I would do for a Malediction invocation, but I'm sure it will come to me eventually.
Death Patron (Warlock)
In some worlds, Death is a God (perhaps also including aspects of undeath), but still makes pacts with warlocks. In others, Death is an entity even the Gods must fear, and one quite pleased to grant powers to warlocks until they come to dwell in Death's Kingdom eternally.
Entities of this type might include Kelemvor and Myrkul in the Forgotten Realms; Nerull and Wee Jas in Greyhawk; Chemosh in Dragonlance; the Keeper and the Blood of Vol in Eberron; and Anubis, Arawn, the Grim Reaper, Hades, Hel, Osiris, and Pluto in real-world traditions.
If you take the Pact of the Chain with this Patron and choose a Raven as your familiar, it gains magic resistance and shares that ability with you.
1st: ray of sickness, spectral leech
2nd: blindness/deafness, mirrored wounds
3rd: bestow curse, meld into stone
4th: aura of hunger, death ward
5th: antilife shell, creation
At first level, when you deal damage that kills creature that is not undead or a construct, you may spend a bonus action or a reaction to harvest some of its departing life energy, gaining one point of Harvest. You may store Harvest equal to your warlock level at any one time. Spend 1 Harvest to reroll all natural 1s in a single damage roll; you must keep the rerolled value. Spend 2 Harvest when you deal damage with a cantrip or weapon attack to increase the damage dealt by 1d8; you may not spend Harvest in this way more than once per turn. Your Harvest pool returns to 0 at the end of any short or long rest.
Memory of Life
At first level, when you cast spells that are restricted to targeting humanoids, such as charm person, you may instead target undead creatures whose CR is equal to or less than half your level.
Starting at 6th level, you gain resistance to necrotic damage and advantage on saving throws against necromancy spells.
As an action, you can change your appearance to be indistinguishable from an animated skeleton. This illusion stands up to extensive scrutiny, but can be revealed with true seeing and can be dispelled as a 3rd-level spell. The illusion ends when you die, or when you dismiss it as a bonus action. Your skeletal appearance does not accurately reflect wounds that you receive, so Wisdom (Medicine) checks to treat you cannot succeed while the illusion is active.
Starting at 10th level, you may spend a bonus action to make an offering to Death. The next time you deal damage to a creature, if dealing double that amount of damage would kill the creature, the creature dies. (Multiply the damage dealt by two, don't roll.) Treat multiple attacks from Extra Attack, multiple rays from eldritch blast, and similar single-action damage as a single damage total. If dealing double that amount of damage would not kill the creature, it takes the normal amount of damage from this attack, and you take that amount and type of damage as well. You may apply any resistance you possess to this damage; any immunity you possess is reduced to resistance for this effect. After making this offering, if a minute passes without you dealing damage to another creature, the offering ends with no effect. Once you use this ability, you may not do so again until you complete a short or long rest.
Starting at 14th level, you may spend a bonus action to gain the life-draining power of the undead. This is a Concentration effect that lasts up to one minute. During this time, when you deal damage, your target's maximum hit points decrease by the same amount. If your target's maximum hit points drop to 0, it dies. If you kill a humanoid in this manner, it rises on the following round as a vampire spawn (not a warrior vampire or spellcaster vampire) under your control. It acts on your initiative count. The vampire spawn dies when its hit points reach 0, or when you take a short or long rest. Once you use this ability, you may not do so again until you complete a long rest.
Design Notes on the Patron
Okay, there's a lot going on here. Meld into stone and creation are kind of odd choices on the Expanded Spells list - the first is an impromptu self-burial or immurement, which seemed like an interesting idea and kept me from writing another new spell. Creation calls out in the spell description that it is an illusion building objects with threads from the Shadowfell, which is perfect for my purposes here. Everything else on the list should be tolerably self-explanatory.
Bleak Harvest is a little on the kludgey side, since it creates a new currency to track. On the other hand, rewarding death-aligned warlocks for murdering things seems pretty on-point to me, and it's often more hacky to do such a thing sans currency.
Memory of Life is there to give the warlock a second set of benefits when fighting the undead, since Bleak Harvest doesn't work on undead or constructs. If you're spending a lot of time fighting constructs... well, you have your other spells for that kind of thing. It doesn't do anything if you didn't pick up charm person, hold person, or dominate person (not that that's a standard warlock spell... I'm not sure why, but it's locked to Archfey and multi-classers; especially weird given that dominate monster appears on their Mystic Arcana list). Anyway, I'm not completely happy with this ability either, because you have to buy something else to get any use out of it.
Shrouded Soul fits in with the many defensive/utility powers found at 6th level in other Patrons. The "disguise as skeleton" thing is chiefly an artifact of how I described things in my own game, but as a "ribbon" (to use WotC's design parlance), it's not like it hurts anything to include it.
Death Offering is an ability that Samhaine helped me brainstorm. It's a gamble intended to work as a finishing move. Whether or not it's fun depends in large part on whether the DM gives good descriptive feedback on how injured the enemy appears to be, and might reasonably lead to enemies who know about this power faking more serious injury to draw a failed Death Offering. Setting it to once-per-short-rest, rather than taking this risk whenever the hell you want, is an overabundance of caution on my part - I'd certainly be curious to see if it's okay as an at-will option.
Reaping Hand draws heavily on undead themes, since several undead get something similar, but always-on. If nothing else, it's a good way to screw over regenerating creatures, because the "big" effect of creating a vampire spawn is going to get fouled most of the time (by loss of Concentration, or duration running out before you can seal the deal), unless you go to great lengths to set it up. When it does work, though, having a vampire spawn until your next short or long rest is crazypants good. It's a rough draft, in any case.