I have this idea for a character similar to a sin eater. Ideally, I would like to create a home-brew spell called Absorb Sin,  which can be described as such:

At the cost of x ( this could be something like a certain amount of necrotic damage and levels of exhaustion),  and at a range of no more than 10 feet, the spell allows the  Sin Eater  to absorb the sins from the soul of the target. I imagine this looking and feeling like the sins are a smoke -like substance drawn out of the target and  inhaled through the Sin Eater‘s mouth. Essentially, purifying the target’s soul. The more evil the soul, the greater the consequence to the Sin-eater (II would have to creat some kind chart with the caveat that the DM will assign the level of evil to the target. For example, a child that steals food to prevent starvation might only cause 4 hp of normal damage; but a sadistic torturer would cause 20 Necrotic damage and three levels of exhaustion to have their soul cleansed of evil … or something like that ).

 At the end of the process of recovering from absorbing the sins of the soul, the SinEater will violently vomit up what a dark, prickly, red and black phlegm-like mass clinging. The greater the sins absorbed the larger the mass. As this repulsive mass falls to the ground, it will bubble and sizzle before finally shrinking into dessicated lump that crumbles to dust before it is whipped up into the clouds like a dervish on the wind.

mount of necrotic damage and exhaustion, the spell allows the caster to absorb the sins of a being from their soul. The more evil the soul, the more necrotic damage and more exhaustion the sin-eater will experience (refer to chart). At the end of the process of recovering from absorbing the sins of the soul, the SinEater will expel what appears to be  a dark red and black phlegm-like mass clinging to a knot of thorns. As it touches ground, this mass will bubble and sizzle before finally shrinking into desiccated lump that crumbles to dust before it is whipped up into the clouds like a dervish on the wind.

what I need help with is determining a reasonable range,  determining the most appropriate school of magic, creating the chart, deciding how it should scale up in terms of power / how much sin can be purified, determining what level this spell should be available in it’s weakest form, determining if it should require an attack and/or saving roll and whether or not it should require consumable elements (and if so, what the value and rarity of those elements should be). I do not want this spell to be game breaking. I am VERY open to suggestions. 

I like a lot that idea and the theme around it but I have some points to considere here. Please take this as suggestions not as critisism.

1. This seem's to do not have any mechanical porpouse more than theme. I mean, in the way you put, it seem's like it just have a negative result on the user of that effect, but no result in the target. So, It seems to me a effect that just reinforce a character flourishing more than have an impactfull use within the game. The "purifying soul" is a nice result, but thats have no mechanical use in the official rules, so I think it probablly must have a houserule on what have a soul purified would impact that character in the game (I assume that you may have this, but since you did not mention it I just stick my attention on this).

2. It seem's more like a feat or trait than a spell. I mean, as a 2nd or 3rd level spell, the caster would need either spend a spell slot, provide some components and have that HP cost. Also, what kind of magic would make that? Would be from necromancy school? Who should be able to do that? a warlock, a wizard, a sorcerer? I think that kind of effect and concept fits more into a deity related ritual or ceremony (pretty close to a exorsism, but of a sin and not a demon) so I would encourage you to make this as a feat for a cleric, or a trait for a themed race (aasimir?). Although I think I pretty nice cleric subclass could be built entyrely from that concept.

Those put togheter, no matter if you keep your original idea or see a fit for my suggestions, I would say that the range on that effect should be probably "touch". I would either put a WIS DC for a unwilling target in order to avoid the effect. So, what I would do (and I'm certainly keeping that idead as a inspiration for my tables maybe):

1st. Defining a need: Houserule that sins have a mechanical effect on PC or NPC. It could be something like a possession for a ghost or a desease effect. It can maybe turn that character vulnerable for possessions or demon charms. Whatever like that:

Sin.

A creature that have sin might be negatively affected as a punishment from the gods. The effect of a sin can vary over the sin scale as the DM descrition. For exemple, a sin as stealing from the poor can make a character be overwhelmed by guild, having trouble to sleep (maybe it don't recover from exhaustion after a long rest), since a sadistic tourturer may be hounted by spirits, become a compulsive murderer or become susceptible for being possesed (disadvantage on saves to avoid that kind of thing). * The sin can be scaled into some levels.

2nd. Define a effect to counter this: that this spell comes to play, but I would rather make it a feat or a cleric subclass: In order to purify those souls and free them from their suffer, some people have powers (misticaly granted by their deity) to eat that sins:

Feat: Sin Eater

Your are granted the power to eat the sins from other people. As an action you touch a creature affected by a sin and free it from the effect. If the creature are unwiling, it must make a WIS saving throw against a DC equal to 8+proficiency+WIS (spellcasting DC), being freed from the sin effect in a fail.

After eat the sin, you might feel nousea until you vomit the sin and take one point of exhaustion at the start of your next round. You can hold the vomit to avoid the exhaustion, to do so you must make a CON saving throw at the start of each of its subsequent turns agains a DC defined by the sin level, holding it in a success.

I have this idea for a  Sin Eater character and would like some ideas/ suggestions/input for a scalable spell designed to do what a Sin Eater does: purify the soul. Mainly, I need suggestions regarding:

- how to scale it up

- what school of magic it should originate from

- whether or not it requires attack roll, whether or not it should have saving roll (and what the save roll should be)

- whether or not it should require consumable element (s) and if it does include consumable elements, what the total cost of the element(s) should be

- ideas for the chart I will refer to in the description of the spell. This chart will basically identify levels of evil/depth of sin from lesser to greater; and it will assign a toll (to the Sin Eater after consuming the spell) to each level. For example: the consumption of the sins of a liar whose lies hurt others = 5 hp regular damage and a 3 hours of exhaustion. Meanwhile, cleansing the soul of something like an Aboleth would reduce the Sin Eater to 1 hp (all of the damage being necrotic) *and* cause them to be unconscious for three days and suffer 3 levels of exhaustion upon awakening.

This is what I have on the spell so far:

                                  **Absorb Sin**

(can also be cast as a Ritual)

**school**: ?

**casting Time**:  15 minutes as a ritual. Otherwise it is instantaneous

**Requires concentration**

**duration**: permanent or until dispelled by the caster

**Range**: ?

**Elements**:  Kinetic and ?
**Effect**:This spell,  allows the Sin Eater to absorb the sins of the target,  thereby purifying the soul so that it may pass into the afterlife designated for those free of evil. It DOES NOT require the target to be dead. The target may be alive, undead, or within 2 hours of death.

The Sin Eater will select a target within within a visual range of *X* feet,  while tracing the shape of an ancient arcane rune in the air and simultaneously  opening their mouth. The sins of the target will manifest as writhing, diaphanous tendrils stemming from the head and chest  of the target. The greater the evil of the sins, the darker the colour of the tendril. To the onlooker, it appears as though tendrils of sin are being sucked into the mouth of the Sin Eater.

This spell comes at a toll to the Sin Eater: the cost of *X number of hp* in *X type* of  damage and *X* hours/levels of  exhaustion, is in proportion to the depth of sin. Basically, the greater the sin, the greater the toll.

At the end of the process of recovering from “consuming” the sins of the soul, the Sin Eater will vomit up something which appears to be a prickly, dark red and black phlegm-like mass. As it falls to the  ground, this mass will bubble and sizzle before finally shrinking into desiccated lump which crumbles to dust before it is whipped up into the clouds like a dervish on the wind.

**Note** As the Sin Eater’s strength and experience increase, they will be able to absorb sins of increasing evil . (Refer to the Tolls of Sin Chart)

Thanks so much for your reply. It looks like the post I thought I had not successfully posted actually did post, here. So if you see a second post on this topic, you can ignore it. Lol

Anyway, I also thought maybe this should be a feat not a spell, after I posted the thread. So, thanks fo confirming that. You are correct in stating that this is very much more about flavour. However, I did think that it could be used on evil servants of evil gods as a means of preventing them from accessing any reward from their evil god. Almost as if their God /Evil Patron /Evil Demon Lord can not recognize them without the stain of evil on their souls. 

but, yeah … to make this more useful than flavourful, I really should make the very evil Targets experience some unsavoury effect. Perhaps a type of disorientation, or feeling physical drained by the experience. Perhaps the sin actually comes attached to pieces of the soul and, the target suffers disadvantage to any  constitution or wisdom rolls and saves. What do you think of that?

Quote from Nichtalisman >>

Thanks so much for your reply. It looks like the post I thought I had not successfully posted actually did post, here. So if you see a second post on this topic, you can ignore it. Lol

Anyway, I also thought maybe this should be a feat not a spell, after I posted the thread. So, thanks fo confirming that. You are correct in stating that this is very much more about flavour. However, I did think that it could be used on evil servants of evil gods as a means of preventing them from accessing any reward from their evil god. Almost as if their God /Evil Patron /Evil Demon Lord can not recognize them without the stain of evil on their souls. 

but, yeah … to make this more useful than flavourful, I really should make the very evil Targets experience some unsavoury effect. Perhaps a type of disorientation, or feeling physical drained by the experience. Perhaps the sin actually comes attached to pieces of the soul and, the target suffers disadvantage to any  constitution or wisdom rolls and saves. What do you think of that?

 I like those ideas but maybe just disadvantage is a bit low reward for the high cost for the trait. I would keep atention on that. So, I think that any effect on the target migth worth that result, you know.

One option I like is what you said about "preventing them from accessing any reward from their evil god". Maybe that trait can be used to deny a warlock or evil cleric to use spell slots for a couple of turns. I think that fits the flavour you wish and also have a equivalent impact on having a exhaustion/dmg cost.

If you keep the idea on leveling sins, you can have that scale to the results. For example: the target have a sin score 4 (let's assume thats a high one) so it maybe lost spellslots in a combination up to 4 levels (like 4 of 1st or 2 of 2nd and so on), but the sin eater takes 4 times dmg (it can be a d6 of necrotic). Also, I'm just make an exemple and I'm not sure if that combination are balanced.

OR YOU CAN GO BACK TO THE JUST FLAVOUR

In that case, I would mess the things a lil bit in order to make that an appealing feat. So, the target suffers no effects on "losing its sin", but the sin eater must have a beneficial effect instead. It can be for example: You touch a evil creature and force them to make a WIS save. In a fail, you eat one of the targets sins and gain X(the sin lvl)d6 temp hit points for 1 min. Until you have this temp hit points you feel nausea and a rotten taste in your mouth. After 1 min, or when you lose all those temp hit points, you gain 1 level of exhaustion. Edit: that option here fits nice as a spell instead of a feat.

Oh, wow! You have some really cool ideas. I am going to have to put more thought into it, for sure. I think the most difficult part is determining reasonable sin to toll ratio. Especially since sins can range from telling a single small harmless lie to a lifelong pursuit of repeated sadistic torture and murder. I think, for the purpose of this, I may have to add the caveat that “true sin is borne of an intentional action *meant* to cause harm or suffering for reasons that do *not* lead to a greater good” even with that caveat, I think determining levels of evil, may be difficult. Once again, I am open to suggestions if you have an idea for how many levels of evil their should be and an example of what each evil might look like. I imagine an aboleth or chaotic evil deity of torture and massacre would be an example of the worse kinds of evil.

Yeap, thats where you must have the harder of the work. Since alligment on DnD are more for roleplay than have a mechanical impact you must built up a mechanical use for that. So, what I can suggest you is to built a table for that "sin scale" but in a way that make it simple. Don't put a high range on this, 1 to 3 or 1 to 5 is enough. It will be better to reflect this on the results of the feat/spell.

I do agree with you on keeping that caveat. I mean, "steal for prevent starvation" is not a sin lol. And that's a important topic: if other use that homebrew from you, you may be clear on how to evaluate that sin level, since it can rely on each personal moral standards.

What I would do to make it simple is to avoid that sin scale. Keep the idea that the feat/spell can "eat" a piece of all the target sins, so any value granted (temp hp/DC/dmg/etc) would be fixed. But that have a bit of loss of flavour :/

Another thing I forgot to mention before; if you make it a feat, keep a limit of uses per long rest. I think that could bring a lot of troubles if its unlimited.

So, I worked on the Sin Eating feat, more; and I would love to see what you think of it. 
 
Here it is:

Feat: Sin Eating      

Prerequisite: You must be either a Cleric, a Paladin, or a Necromancers of good alignment

Number of uses: 4 per long rest

Description:  You (the Sin Eater) may use a bonus action to purify the soul of a single, visible target, within 25 feet of you. The target must make a wisdom saving throw; on a failed saving throw, the target suffers all the damage  effects but none of the purification indicated on the Sin Eater’s Chart (see below). On a successful save, the target suffers only half damage and their soul is not purified. However, the Sin-Eater,  also does not experience a toll from purifying the soul through consumption.

Sin Eater’s Chart

**caveat** the DM has ultimate say when determining the level of evil of each target. 

What Sin-Eating looks like to the observer:  The person eating the sin will look at the single, selected target as they open their mouth, wide while deeply inhaling. As this happens, the sins of the target will emerge from the target’s head,eyes, hands, loins, and chest,  as dark, writhing tendrils of smoke. These tendrils will appear to rush into the Sin Eater’s mouth, at which point the Sin Eater will close their mouth. Throughout this process, the target will be  suspended about 4 ft above the ground, as if nailed to an invisible cross. The moment the sins have entirely left the target’s body, the target will drop to the ground. Note: the opening of the mouth, the inhalation, and the closing of the mouth are simply part of ancient custom. In actuality, the sins would be drawn to the sin eater upon a thought.

What recovering from eating sin looks like:  After paying the toll of consuming the sins of a soul, the Sin Eater will violently projectile vomit a dark, prickly, red and black phlegm-like mass. The greater the sins absorbed, the larger the mass. As this repulsive mass falls to the ground, it will bubble and sizzle before finally shrinking into dessicated lump that crumbles to dust before it is whipped up into the clouds like a dervish on the wind.

I think that's getting a fine shape. Personally I still think it's maybe a bit OP and mechanically complicated.

I would make some adjustments in order to balance and simplify it (but that's just what I think would work better within the game considering a regular table):

1st. Personally I think that 4 uses is to much at low levels, so I would make it based on proficiency bonus instead of a fixed value.

2nd: I think it have a huge impact and have a pretty nice flavour for being just a bonus action, so I would make it an action.

3rd: I think the table are a bit overwhelmed and can be difficult to DM and Players to track the effects, so I would simplify the damage scale based on the level of the sin. Also I would put it as a d10 to addapt that lower scale.

4th: I would simplify the toll and vary only on its duration. Also, I would make a mechanical use on "clean the soul's evil" forcing it to become neutral (which would make the roleplay of that NPC changes). That mehcanical use on the alligment would justify the toll beyond just being a damage dealing feat.

How it would become:

Feat: Sin Eating (Here I would change to "Sin Purification" since the user isn't exactly feeding on the sin, but that's just personal and the name you have is pretty nice though)    

Prerequisite: You must be either a Cleric, a Paladin, or a Necromancers of good alignment

Number of uses: you can use this feature a number of times equal to your proficiency bonus per long rest.

Description:  You (the Sin Eater) may use an action to purify the soul of a single, visible target, within 25 feet of you, that have a evil alligment. The target must make a wisdom saving throw against your spellcasting DC. On a faild save, the target suffers radiant damage in a number of d10 equals to the sin level (see the table below) and its alligment becomes neutral as its soul is purified from its sins. In a successful save, the target suffers only half damage and its soul isn't purified.

Toll: If the target fails and have its soul purified, the Sin Eater becomes tolled and must reduce a number equal to the sin level (see the table below) for any attack roll, saving throw or abillity check until the end of its next turn. The sin level must be determined by the DM according to the Sin Table.

Sin Tabel

Level	sin exemple
1	Violent. Attempt willingly against the peace and the life of people.
2	Disorder. Spread discord; manipulate people; Corrupt governments in order to cause harm to entire vilages, towns or cities.
3	Torturer. Murder with greater violence; Enjoy to cause suffering.
4	Profaner. Desecrate temples and holy sites; act systematically against a deity or faith and its followers.
5	Evil Agent. Deal with and act in favor of a greater demon or evil creature;

**caveat** the DM has ultimate say when determining the level of evil of each target and can increasce the level range to better acertain the evil nature of some creatures. For exemple a daity or a greater demon of true evil nature might have a higher level than 5.

What Sin-Eating looks like to the observer:  The person eating the sin will look at the single, selected target as they open their mouth, wide while deeply inhaling. As this happens, the sins of the target will emerge from the target’s head,eyes, hands, loins, and chest,  as dark, writhing tendrils of smoke. These tendrils will appear to rush into the Sin Eater’s mouth, at which point the Sin Eater will close their mouth. Throughout this process, the target will be  suspended about 4 ft above the ground, as if nailed to an invisible cross. The moment the sins have entirely left the target’s body, the target will drop to the ground. Note: the opening of the mouth, the inhalation, and the closing of the mouth are simply part of ancient custom. In actuality, the sins would be drawn to the sin eater upon a thought.

What recovering from eating sin looks like:  After paying the toll of consuming the sins of a soul, the Sin Eater will violently projectile vomit a dark, prickly, red and black phlegm-like mass. The greater the sins absorbed, the larger the mass. As this repulsive mass falls to the ground, it will bubble and sizzle before finally shrinking into dessicated lump that crumbles to dust before it is whipped up into the clouds like a dervish on the wind.

Well, thats just my suggenstions close to how I would play this if it was my tables. I think that simplifications saves a bit of confusion and make it more balanced with the official feats. You can addapt what you think its worthy from this on your idea but also can ignore if thats running out of your porpuses.

Thanks, again for all your great input. I like your sin categories. Also, a friend reminded me of a little spell called alignment change, which I could just flavour to appear as though my character were consuming the sins of an evil soul (or the virtues of a good soul, if that were the case). Which makes this thread an interesting and fun exercise; but ultimately moot. But I really do appreciate your comments, as they help me to better understand which elements to consider when I want to make a new feat