What level should this Burning Words spell be?

Question

I've created this spell with the help of one of my players, and would like some input on how balanced it is and what level to put it at. Thanks in advance!

Burning Words (and/or Epic Burn)

nth level enchantment

Casting Time: 1 action
Range: 60 ft
Targets: A creature that can see and hear you within range
Components: V
Duration: Instantaneous
Classes: Bard

You speak an insult at a creature you can see and hear within range. If the target can understand you, it must make a Charisma contest against you. If you win, the target takes 3d10 fire damage and 3d10 psychic damage, however, if you fail, you take 6d10 fire damage and 3d10 psychic damage.

Answer 1

This is not attractive at any tier of play

Your chance to die: If it backfires, you take 9d10 damage, on average 49.5. You still have 1% chance to take 70 or more and could take up to 90. A typcial Bard has d8 hit points per level. Even with max hits in level one, 5 hits per additional level and a light Con bonus (Bards need high Dex due to light armor, so unlikely to be better than +1), you would need to be 13th level or higher to cast this with a reasonably low risk of dying, and 17th level to survive for sure, assuming you are at full health. You would never want to cast this at low levels.

Your chance to win the contest: What is your chance to win the contest? The Bard will have +5 bonus to Charisma ability rolls from level 8 on if they maximize their Charisma, as typically is done, and get Jack of all Trades, so a total +7 from level 9, and +8 at best. The average CHA bonus in the Monster Manual is +0, however monsters of CRs greater then 10 tend to have a bonus more in the +3 to +4 range.

By the time the bard could use this without significant risk to die, the margin is about +4 away from an even 50/50 chance. So your expected result is dealing 6d10 (33 at face value, many monsters have fire resistance, espcially at higher levels, so in practice you can expect about 30 damage) 66% of the time and eating 9d10 33% of the time. Overall, you would expect to deal next to nothing net with this (about 3 points).

Now, you can of course pick and choose whom you use this against, and if you can figure out which monsters have low Charisma you can improve the odds. But outside of a couple deplorable (and typically weak) monsters with negative Charisma boni, even in the best case of +8 on the contest, your odds would be only about 80% to win vs 20% to lose, and you only get to deal 14 points more than you expect taking.

Your expected pay-off: So in effect, you risk dying for the chance to net make 3-14 points of damage. There is no spell level where this becomes a good deal, not even on level one.

Bards already have few spells to pick and having narrow ones is not the way to go for them. This spell is as Thomas says, useless and a bad choice to try on any level of play.

The design is not a good fit for 5e: As an added note, 5e in general does have very few spells with adverse effects on the caster in case of unlucky rolls (Contact Other Plane or a botched Teleport, are about as bad as it gets). The swingyness of the outcome here creates a powerful effect that could deal damage in amounts one would expect maybe from a level four or five spell, but low net benefit would point towards a much lower level spell, even if the numbers are tweaked. In general, anything swingy is to the disadvantage of the characters, as they will be in many, many combats, while the typical opponent is only in one against them. 5e is aiming at more predictable combat outcomes, with larger amounts of hit points, and fewer save-or-die effects than older editions of the game.

Answer 2

I would never use this, no matter the level

The design of this spell is highly problematic. The risk you undertake when you cast this spell is too great. If you lost the contest, you take a total of 9d10 damage (average 49.5). That is a huge chunk of hit points. It simply isn’t worth the risk of getting unlucky and torching yourself for 50 hit points when the upside is 33 points of damage to the target.

Answer 3

The tradeoff is too large to justify using at any level

As mentioned in other answers, hit points are a very valuable resource in this game. If you're going to use them for offensive purposes (which has not been done in official spells, as far as I know) then they'll need to either give a very strong effect, reflecting how this self-damage could almost kill you instantly. There's also the issue that this self-damage could interrupt any concentration spell you're currently sustaining, which could be a huge loss during a fight.

A possible approach to balancing spells using the existing ones

Most offensive spells in a chosen tier have an "average damage" they tend to gravitate around. The way those spells are balanced around this value without being identical is by adding "modifiers" to them. Those modifiers can be positive or negative :

• Positive modifiers are usually additional effects (debuffs on target, buffs on self or allies, long-term effect in an area or on a target...).
• Negative modifiers are usually conditions that make the spell harder to use (saving throws to reduce/nullify the spell's impact, restrictions on possible targets, damage being dealt over time rather than instantly...).

Usually those modifiers are used in tandem with adjusting the actual damage value, in order to make a spell better in some situations and worse in others. All of that to say, balancing a purely offensive spell means making it stronger than other spells in the same tier in some situations and weaker in other situations.

If you really want to make a hit-or-get-hurt spell, here's an idea of a rebalance of your spell as a cantrip. (note : I have not playtested this cantrip idea, so I cannot guarantee that it is balanced)

The gambler's Vicious Mockery ?

The closest bard cantrip I could find is Vicious Mockery (which, conveniently enough, has identical casting conditions), with the following :

• Positives : target doesn't need to understand you ; 1d4 psychic damage (one of the least resisted damage types in the game) ; on hit, gives disadvantage to the target's next attack roll.
• Negatives : Creature needs to hear you ; has a saving throw ; does nothing on a successful saving throw.

With that in mind, let's go over each of those elements (keeping damage for last), and how to modify them according to your spell idea :

• Target doesn't need to understand you : this one is a bit difficult, because it depends heavily on your DM and the kind of enemies you'll face. Having the need for the enemy to understand you would be nothing more than flavor in some settings, while it could make the spell near-useless in other settings. For the sake of keeping it on par with Vicious Mockery in terms of possible uses, I'd either keep that in, or make it so that the spell makes it possible for the target to magically understand the meaning of the words linked to the spell.
• Giving disadvantage on the target's next attack roll : this is what gives the spell flavour and utility, and is also what makes the cantrip unique. Removing it means removing a strong aspect of the spell, so we'll need to compensate later.
• Creature needs to hear you : mostly flavour, the implications are very rare. We can keep that in.
• Saving throw : here, the saving throw is the key component of our spell's "gambling" aspect, so it makes sense to keep it as you mentioned it. I'm unsure of the balancing implications of having it be either Charisma or Wisdom, this might be worth a question of its own.
• When the target's saving throw is a success : and here's the spell's second key component. Dealing a small amount of damage to the user on failure will introduce the "gamble" aspect properly. The damage in itself doesn't need to be incredibly high, a simple 1d4 of psychic damage would be enough, especially since the damage could break concentration. Alternatively, you could make it so that the self-damage is higher (1d6 for example) but does not create concentration checks.

Finally, the damage itself. To balance out the conditions and risks of using this spell, we need damage high enough to make the player hesitate between this spell and other alternatives. Keeping the psychic damage type makes sense with the spell's theme, but it's also important to note that fire damage, while effective early on, is one of the most resisted damage types later on. Because of this, my proposition is to give this spell the following damage and scaling :

• Base damage : 1d4 psychic + 1d6 fire (1d4 psychic self-damage on fail)
• At 5th level : 1d4 psychic + 2d6 fire (1d4 + 1 psychic self-damage on fail)
• At 11th level : 2d4 psychic + 2d6 fire (1d4 + 2 psychic self-damage on fail)
• At 17th level : 3d4 psychic + 2d6 fire (1d4 + 4 psychic self-damage on fail)

This kind of trade-off spell could work better for prepared casters

As a bard, you already have very limited spell choices. Because of this, it will be much more difficult to make "tradeoff" versions of spell work, since you usually can't have both of them at the ready to make the choice of which one to use depending on the situation. However, I could definitely see this concept for a spell working on a "prepared" caster.