Other uses for 5e Hit Dice

Hit Dice in 5e seem underutilized as a resource. I have no idea if this is intentional design, but here are some other possibilities.

• To power class abilities.
• Berserker barbarians' Frenzy ability could burn HD instead of causing exhaustion.
• A paladin's lay on hands ability could let them spend HD on another's behalf. That seems a little more sacrificial to me, and is swingier that picking an exact number of HP.
• Probably some sorcerer abilities, but who cares.
• Maybe a warlock invocation that lets you burn HD into spell slots. Seems like an appropriate risky sacrifice for power for that class.
• Magic item fuel. I did this once already.
• You could make attunement to an item in general require investing a HD in it, if you wanted to reduce magic item use a bit.
• Healing potions that let you spend hit dice would scale automatically to the character using them, based on HD size and Con modifier.
• Ring of X-Ray vision could eat HD instead of inflicting exhaustion.
• Instead of reducing max HP, damage caused by certain undead could also use up a hit die. They come back on their own at a long rest already, so no special rules needed on the monster. If the undead can create spawn, they do so by killing a creature with no HD remaining.
• Potions that restore HD.
• Diseases could eat away at HD.
• Spells that allow HD to be used, like 4e healing surges. Healing Word seems like an interesting candidate.

Path of the Pact-Maddened

Whispers and promises from impossible voices drive the pact-maddened barbarian into a supernatural frenzy. They surprise their opponents by weaving arcane magics among their formidable physical prowess.

When you first choose this path, choose a patron from the Warlock class.

3rd level - Pact Magic

You can cast a small number of spells granted by your patron. Charisma is your ability modifier for these spells.

You learn a warlock cantrip of your choice which you can cast at will.

You learn a warlock invocation of your choice.

You can cast one of the 1st-level spells from your patron's expanded spell list. Choose which at the time of casting. Your spell slot level is 1 when you cast a spell this way. Once you use this feature you can't use it again until you finish a short or long rest.

At higher levels more spells from the extended spell list become available, and your spell slot level for all such spells increases.

• 6th level - 2nd level spells become available, and your spell slot level becomes 2. You learn a warlock invocation of your choice.
• 10th level - 3rd level spells become available, and your spell slot level becomes 3. You learn another warlock cantrip of your choice.
• 14th level - 4th level spells become available, and your spell slot level becomes 4. You learn a warlock invocation of your choice.

3rd level - Conduit of Rage

You can cast warlock cantrips while raging, and add your barbarian rage damage to damage dealt by your warlock cantrips while doing so.

Casting a warlock cantrip counts as attacking a hostile creature for purposes of maintaining your rage.

6th level - Paroxysm

If you hit with two melee weapon attacks using Strength in a single round, you can use your bonus action to cast a warlock cantrip.

10th level - Lucid Rage

While raging, you may cast an available spell from your patron's expanded spell list. Doing so counts as attacking a hostile creature for purposes of maintaining your rage. (This is a separate spell than the one granted by Pact Magic.)

Once you use this feature you can't use it again until you finish a short or long rest.

14th level - Induct by Force

If you score a critical hit while raging, the target must make a Charisma saving throw (DC 8 + your Charisma modifier + your proficiency bonus). If it fails, it becomes charmed by you.

The charmed target must use its action before moving on each of its turns to make a melee attack against a creature other than itself that you mentally choose.

The target can act normally on its turn if you choose no creature or if none are within its reach.

All charm effects end when your rage ends. Also the target can make a Wisdom saving throw at the end of each of its turns. On a success, the charm ends.

Metastus

Here is an NPC party led by a disease-infatuated mage, Metastus. There's a sprinkling of OSR in here, as some of the mage's daily spells have been removed to grant resistances and a weird magic effect of becoming an infection upon death.

Voice suggestions are provided for each NPC.

Metastus

Metastus is not immediately hostile to the party, but he is not a pleasant man.

The mage Metastus is infatuated with disease, both its infliction and its treatment. He appears as an older man in a dingy, off-white cloak with sparse hair to match. His skin is pallid and parchment-like, and he has no mustache or beard because he has no lip or chin, their having rotted off in some failed experiment years past.

His knowledge of sickness has won him many wealthy patrons through his treatments. In their turn he has extracted many favors and subjects. He never willingly lets a patient perish, but he will also infect a subject with an unknown strain in order to test the efficacy of his treatments.

He meticulously records all phases of his patients' endeavors. The results of his experiments are usually shared with colleges and hospitals through the land. He is eager to hide behind this fact when defending anything which might be interpreted as a depredation. He adopts an air of clinical detachment during these times but just below the surface he enjoys dancing people along the line between life and death.

Voicewise: leave Professor Farnsworth and Peter Lorre in a sauna for a few decades until they melt together and forget their lips.

Metastus

Medium human, Lawful Evil
Armor Class 12 (15 with mage armor)
Hit Points 40 (9d8)
Speed 30 ft.
STR DEX CON INT WIS CHA
9 (−1)  14 (+2)  11 (+0) 17 (+3) 12(+1)  11 (+0)
Saving Throws Int +6, Wis +4
Damage Vulnerabilities fire
Damage Resistances piercing and slashing from nonmagical attacks
Damage Immunities poison
Condition Immunities poisoned
Skills Arcana +6, Medicine +6
Senses passive Perception 11
Languages Common, Elven, Orc, Deep Speech
Challenge 6 (2,300 XP)
Spellcasting. Metastus is a 9th-level spellcaster. His spellcasting ability is Intelligence (spell save 14, +6 to hit with spell attacks). He has the following wizard spells prepared:

• cantrips - acid splash, light, mage hand
• 1st (4 slots) - charm person, grease, sleep
• 2nd (3 slots) - ray of enfeeblement, web (of sputum)
• 3rd (3 slots) - dispel magic, stinking cloud
• 4th (3 slots) - black tentacles, noxious form
• 5th (1 slot) - contagion

Equipment: slippers of spider climbing, wand of the war mage +1, cloak of protection (+1 AC and saves)

He is infectious. If he is slain he can use a reaction to infect one person with a disease that will slowly turn the victim into him (Constitution save to resist). It will manifest first as the ability to cast some additional spells he knows.

2645 GP, 110 PP in a chest in his lab.

Noxious Form: 4th-level wizard spell. As gaseous form, but a creature who enters your space or starts its turn there are affected as if by stinking cloud and take d6 + your spellcasting ability modifier acid damage. You are unaffected by stinking cloud while in noxious form.

Spellbook: Memorized spells plus stinking cloud. The necessary course of treatment to preserve Unction's seething life.

Nutch-Nutch

Homunculus (MM 188)

Metastus' familiar. Balloon-like, with tiny wings, a puffy face, wiggly hands and feet, and an unfortunately placed stinger. Deflates into a snake-like creature with grabbly spindle claws.

Voicewise: Like a farting helium balloon.

Drathe

Nothic (MM 236)
Equipment: Cloak of Elvenkind

Metastus' companion of many years. The mage provides it access to any libraries he is welcomed to. In return, the creature plies minds encountered for secret, shameful sicknesses of a family which can be used as leverage in negotiations.

It has gazed at the mage in his sleep and enjoyed what it found in those gray dreams.

Voicewise: Only speak while inhaling and pretend you've got sandpaper next to your gums.

Unction

Orog (MM 247) except:
AC 20 (plate and shield)
HP 51
Equipment: sword of vengeance - longsword, +7 to hit, reach 5, d8+5 damage.

martial adept - d6 superiority die. goading attack, pushing attack (PHB 74)
parry - reaction - adds 4 to AC against one melee attack that would hit. must see attacker and be wielding a melee weapon.
Probably challenge 3?

This orog was offered into Metastus' service by a tribe of orcs whom he gifted with a maddening plague which allowed their warriors to crush a neighboring tribe before their lungs exploded. Their ravening spirits inhabit his gleaming bronze blade.

He has long stopped questioning the motivations of Metastus' company and is confident he and the mage together can face down any threat. However, an open display of hostility means he'll try to throw the offenders off the nearest ledge or alert his companions if none is available.

Metastus knows Unction has no sense of honor and so has, over the years, set up a complex system of disease and treatments within the orog to ensure his loyalty. Without a seemingly random administration of herbs and extracts known only to the mage, he would die a painful and gasping death within days. With practice and desperation he has learned many techniques to protect Metastus' life as his own.

At the moment he abides a suppurating throat affliction requiring a Constitution check (DC 10) to voluntarily make any noise louder than a whisper - a failure stuns him for a round as he hacks up volumes of loose, bloody phlegm.

Voicewise: Grisly-wet, like a raw steak has taken offense to your ability to move around without its consent.

Aubert

Guard (MM 347) - Neutral. Immune to disease.

A simple farmer whose village was struck by an unusual plague to which he was apparently immune. Metastus offered to save his kin in exchange for his servitude, and he readily accepted.

The process has been gradual - several villagers have been hauled to the band's camp for extended treatment, and drift in and out of weak consciousness. Aubert devotes every waking hour to their care

Aubert hates Metastus for the depravities he has seen, and himself for his part in them, but will take up arms to defend the mage as the last chance to save his friends and family.

Voicewise: 90% stuttering misery, 10% shrieking indignation.