Since our session zero we've included the Potion Miscibility variant rule but never used it 'til now.

The party (lvl 5 now) has hoarded quite a few potions - all common or uncommon level - and only used healing potions. At the end of the last session the alchemist decided they would mix a few together, after a few tries of varying success they rolled 100 on mixing a Potion of Growth and a Potion of Fire Breath.

The rules for rolling 100 on mixing potions is:

Only one potion works, but its effect is permanent. Choose the simplest effect to make permanent, or the one that seems the most fun. For example, a potion of healing might increase the drinker’s hit point maximum by 4, or oil of etherealness might permanently trap the user in the Ethereal Plane. At your discretion, an appropriate spell, such as dispel magic or remove curse, might end this lasting effect.

I ended the session with a dramatic description of their swirling potion - however I'm not really sure how to proceed. The players had a win and I want them to be rewarded for that - I'm just not sure which effect is most balanced. Also, unsure whether "Choose the simplest effect" means DM chooses or the player chooses - may not even be up to me- I've asked that in a separate question. Even if it is the player's choice, an idea of the imbalance this could cause would be useful to discuss with them/prepare myself for.

Permanent Growth: A player gets permanently enlarged - gains a size (medium->Large or small->medium), +1d4 damage to any weapon they were holding at the time and advantage on strength checks and saving throws.

Permanent Fire Breath: A player permanently gets a breath weapon that

A bonus action to exhale fire at a target within 30 feet of you. The target must make a DC 13 Dexterity saving throw, taking 4d6 fire damage on a failed save, or half as much damage on a successful one. The effect ends after you exhale the fire three times or when 1 hour has passed.

I considered making the breath weapon have no time limit, but still only 3 uses. However, that feels like it cheapens the win. I don't want to do that to my players.

As a comparison, they're both like getting a second level spell free...permanently. For fire breath the save is likely lower, but its damage is better than the 2nd level dragon's breath spell - though that is an area effect and fire breath is a single target. Growth is a straight copy of the 2nd level Enlarge without the option to reduce.

Which of these is the most balanced option?

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    \$\begingroup\$ In what campaign is being permanently trapped on the ethereal plane the simplest or the most fun? \$\endgroup\$
    – Kirt
    Mar 12, 2022 at 16:21
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    \$\begingroup\$ @Kirt I imagine it depends on what the other potion was. \$\endgroup\$
    – GMJoe
    Mar 12, 2022 at 21:22
  • \$\begingroup\$ The fire breath is more of a 1st level spell: 4d6 is on average 14 damage. 3d8 (chromatic orb) is on average 13 damage. Also, the permanent growth only makes sense if it adds a d4 to all weapon attacks: why would it just be ones held when the potion is drunk? \$\endgroup\$ Mar 13, 2022 at 16:28
  • \$\begingroup\$ @TheDragonOfFlame My thoughts were that the weapon gets larger too so a longsword gets bigger and is more akin to a greatsword. \$\endgroup\$ Mar 13, 2022 at 21:02
  • \$\begingroup\$ If it were me, I would have rolled on the Potion Miscibility table behind the DM screen if the mixing happened in bottles, and "Unless the effects are immediately obvious, reveal them only when they become evident." \$\endgroup\$ Mar 14, 2022 at 2:56

4 Answers 4


Either effect is going to have repercussions.

Exact balance can be hard to determine

The two effects can be reduced to damage per round, but that's really not going to tell you much about how it's going to affect your characters in your game.

Basically, the character will be getting a magic item. In campaigns with a lot of magic items the addition probably isn't that significant. In a campaign where at level 5 there are no or few magic items, the effect will be greater.

The breath weapon is likely more powerful

For many characters the breath weapon is going to be more powerful, just because it does more damage. However, for a martial character, larger weapons doing an additional 1d4 is significant, and for many characters advantage on strength checks and saving throws would be, well, advantageous.

You need to deal with the issue of a breath weapon as a bonus action

Of significant issue is that the potion of fire breath says you can use a bonus action to breathe the fire. This is a significant feature, if permanent. Some DM discretion is called for here. A permanent breath weapon bonus action is significant, and as a DM I would pretty likely rule that out as a hard no, not happening.

Although, after looking at it, you may find it's not significantly overpowered even as a bonus action. Or perhaps the player is really keen on the bonus action feature. If you want to allow the bonus action but limit it, you could make it usable 3 times daily, which is reasonable based on the original potion. That way they'd get to have it as a bonus action, but there would be some limits.

Other than that, the breath weapon is not going to be outrageously unbalancing

In the end, depending on your game, the breath weapon is probably not going to be outrageously unbalancing (assuming you account for the bonus action), any more than many magic items. After all, the damage at an average of 14 on a failed save isn't extreme, especially since it doesn't scale with level, and depending on how you rule, it costs an action or bonus action that the character can't be otherwise using.

Take the player into account

To me, what the player wants is probably pretty important, and so you might consider discussing with them, so that you can figure out the most fun option.

Good luck!

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    \$\begingroup\$ The potion of fire breath says the attack is a bonus action, not an action. That was where I felt we were adding quite a bit of power. Agree that having it as an action wouldn't be nearly so unbalancing. \$\endgroup\$ Mar 12, 2022 at 13:29
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    \$\begingroup\$ Edited to account for that. \$\endgroup\$
    – Jack
    Mar 12, 2022 at 15:04
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    \$\begingroup\$ There's been a lot of discussion of how a breath weapon might be overpowered if it's a bonus action, but consider the play style and class of the character that you're granting it to. For example, my main is a Swashbuckler Rogue. Having a Breath Weapon sounds cool and maybe OP. But having to pass on my "standard" / "core" Cunning Action bonus action to use it? NOT as OP. That's a toughie. I probably wouldn't use it that often. Especially as I gain more levels, when the Big Bads I'm fighting hit REALLY hard. Is it worth giving up that Disengage for the Breath Weapon? Probably not! \$\endgroup\$ Mar 12, 2022 at 21:43
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    \$\begingroup\$ Yep. That's why I said "it costs an action or bonus action that the character can't be otherwise using", and other comments about the BA. For some characters, giving up a BA is significant. \$\endgroup\$
    – Jack
    Mar 12, 2022 at 22:05

Strike a Balance

If either of the options seems too powerful for you, negotiate down. Try to find a fun balance that works for both you and the player.

For example, the fire breath becomes permanent. But like a dragon, after each use the player needs to recharge it. At the start of each subsequent turn, the player can roll 1d6; on a 5-6 they can use their fire breath again. Otherwise it automatically recharges after five minutes.

Or maybe once per day (long rest) the player can activate the effect of the potion as if they had just consumed it. So 1d4 hours of enlargement. Or three uses of fire breath. Whichever potion you decide is 'permanent'.

Beware enlarge

While both may be second level spells, and the effects may seem somewhat balanced, a sudden and permanent size increase is going to have issues. Finding clothing, rooms, et cetera is going to be more difficult and expensive. While stealth rolls are not automatically hampered, finding cover or hiding spots will be more difficult.

You can just shrug it off as things not covered by the rules, but that may have issues for immersion. You might also fully include all of these hardships, and in that respect say it is more balanced; but the player may not be happy with that.

  • \$\begingroup\$ I started writing an answer which was very much like this one, so I think it's redundant except for this - it might also be fun to have a "flavour" effect that is permanent, like the Enlarged character being a few inches taller than they were (perhaps you might describe them bumping their head on a doorway or having an NPC remark on it), or the Fire Breathing character have some intense (but mechanically harmless) heartburn each day as they "recharge" the effect. \$\endgroup\$ May 18 at 8:42

Be careful with permanent added powers

I agree that the players should get the full win here. A chance of 1 in 100 means taking considerable risk or expense to make the effect happen, and you're right not to cheapen that win. That said, this will be a permanent effect that is quite strong, especially on their level.

What is more fun? Short term, more power is more fun. Longer term, an overpowered ability that makes other abilities pale is not more fun, especially not for the rest of the players. For this reason, I would go for the weaker effect here.

Fire Breath

The breath weapon will add a free bonus action option each round, and bonus actions are not cheap to come by. For example, the Polearm Master feat provides a reliable source for an attacking bonus action, or taking a level in Cleric (War Domain) provides a reliable extra attack as a bonus action. Both are significant investments of character development resources.

How much expected damage is the fire breath worth each round, if it can be used unendingly? 40% of the opponents can be expected to make their Dex save against a caster level adequate DC, at level 5 you would expect a DC of 15, so 50% will make their save on average against DC 13 (and more as you get to higher levels). This means (4d6 * 50% + 4d6 / 2 * 50%), or about 10-11 points of expected damage, less later on.

Against opponents with fire resistance it would be half, of course. Fire is one of the most resisted damage types. On average, you can expect it to make about 90% of its damage across all monsters encountered, or still 9-10 points, less on higher levels.


The main effect is the +1d4 to each attack, on average 2.5 points. If you give this to a fighter, who already has Extra attack at level 5, it will be worth 5 points of damage, multiplied with an average to hit rate of about 65%, about 3 expected damage per round without bonus actions.

In the short term, this is thrice weaker. In the medium term with feats that give a bonus attack it is slightly weaker, although the advantage on Strength checks (such as grapples) and opportunity attacks may make up for some of it. Eventually at high levels, when martials get more Extra Attacks and the fire breath becomes worse, this can be stronger. But that will be very late in the campaign.

There also is a role-playing impact. Firebreathing is fricking cool, but you can hide it. Being enlarged can hardly be hidden. It will create a lot more notority and interesting discussions for the group to have a "giant" as one of their members, as every person at any inn and every peasant can see that.

And, if you turn from medium to large, there are other effects both positive and negative: your carry capacity doubles, another upside. You need to squeeze through 5' passages, and cannot get through more narrow ones. You weigh eight times as much and need to eat and drink four times as much. If a party member can become a giant eagle, can it still carry you? Can others lift you on a rope? Do you fit into a bed at the inn? A lot more interesting than just firebreathing.

For the reasons of keeping it closer to balanced for most of the campaign, and for it being more role-playing fun I would likely go with Enlarge. As the DMG says, though, it is your choice.

  • 1
    \$\begingroup\$ Bonus actions aren't free. There is an opportunity cost of choosing that vs other bonus actions available to the character. \$\endgroup\$
    – illustro
    Mar 12, 2022 at 23:07
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    \$\begingroup\$ I'm not saying the bonus action is free, I am saying the option for the bonus action is free. Of course the bonus action itself has an opportunity cost, and as you get other sources for attractive bonus actions, this weakens the fire breath. But often you need to invest, taking a feat, class levels or casting a special spell like spiritual hammer to get the option for using a bonus action \$\endgroup\$ Mar 13, 2022 at 8:12
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    \$\begingroup\$ How big exactly does Enlarge make you? Do you still fit through doors? Can you sleep in a normal size bed? Is romance with members of your species going to be problematic (or improved)? Since you mention RP impact, there are potential downsides. Also transport/travel logistics, like if one party member can become a giant eagle to carry the rest, does a large creature weight them down twice as much? Can others lift you on a rope? You probably couldn't squeeze through as narrow an opening. \$\endgroup\$ Mar 13, 2022 at 14:43
  • \$\begingroup\$ @PeterCordes Thank you, all good points. I added some of it plus some other rules mechanics impact (nourishment requirements, carry capacity) \$\endgroup\$ Mar 13, 2022 at 15:35
  • \$\begingroup\$ David G.'s answer also has an opinion on some possible downsides, some that seem non-fun. (So you'd have to decide if you're fine with letting magic explain those away, to not create incongruities.) The Enlarge spell wording is: The target's size doubles in all dimensions, and its weight is multiplied by eight. so it explicitly calls out the cubic mass scaling, and that you do fully double, not just to the minimum for the next size up. (The height range for Large is 8-16 ft as per dungeons.fandom.com/wiki/SRD:Table_of_Creature_Size_and_Scale so 2x 6ft is squarely in that range.) \$\endgroup\$ Mar 13, 2022 at 15:39

Remember the Downsides

Potions are designed for short term effects. When you get them permanently, more things might happen.

These effects would be about balancing the change long-term. That is, it might not balance any given combat, but it will give some ongoing costs to help balance out the players life. It also might provide a new quest, as in "How can I get rid of this permanent potion and its downsides?") though the players might phrase it as "How can I get rid of this permanent potion's downsides?")

I think most of what I'm suggesting can be alleviated with money or healing magic.

I will also comment that this isn't about a punishment, just a natural side effect. And I think you probably don't want more than one or maybe two side effects.


If you double (for easy math) the size of the beast, you octuple the mass and quadruple the surface area.

  • This means four to eight times the food needed.
  • This means that he will produce eight times the heat but only be able to easily dissipate four times the heat. He will get heatstroke and heat prostration easily. This could easily be a problem in any sustained combat.
  • This means he will develop back problems, foot problems, and probably lots of other health problems.

Additionally, common folk (like every town you visit) may consider him to be a monster, who might be shunned, or driven out, or even attacked!

Fire Breath

Does the fire wish to get out? If so, and he doesn't use it enough, it might come out on its own. Like belching when trying to sleep. This actually becomes more of a problem when you are sleeping in a town, as you might burn down the (dry, non fire resistant) inn, or burn/kill somebody else in the bed.

Long term use could also have health impact. For instance, it could result in burns in the mouth (requiring extra healing and/or special diet).


Don't (preemptively) warn the players! :-)

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    \$\begingroup\$ Dropping negative effects on players without their knowledge is what is often termed as "a dick move" \$\endgroup\$
    – SeriousBri
    Mar 13, 2022 at 14:12
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    \$\begingroup\$ There is always a solution in DND, doesn't mean you should make problems just because you can. \$\endgroup\$
    – SeriousBri
    Mar 13, 2022 at 14:20
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    \$\begingroup\$ You might want to edit into your answer that the negative effects you mention help create balance. You said it in the comments, but not the answer. Also, you might be able to address SeriousBri's concerns by saying in the answer how your solution makes things more fun. \$\endgroup\$
    – Jack
    Mar 13, 2022 at 14:35
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    \$\begingroup\$ Now I have realised that making my comments in the way I did is also a 'dick move', have some apologies and some more constructive criticism this time: you are right that complications and downsides can lead to fun, but I think the difference is that when a player sees a shiny (which this buff is) and then you hide a gotcha, it takes the fun out of the acquisition of that shiny. It is ok to give players things and have those things lead to predictable complications (IE: they get a powerful item that everyone covets and tries to steal) but no player is going to expect back ache for example. \$\endgroup\$
    – SeriousBri
    Mar 13, 2022 at 15:31
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    \$\begingroup\$ Exactly double isn't just easy math, it's literally what the Enlarge spell says it does, including square/cube law mass scaling: The target's size doubles in all dimensions, and its weight is multiplied by eight. It is a magic effect, so you don't need to use accurate physics / biology to figure out ensuing problems like the heart pumping blood all the way to the head, or over-heating. Those could easily be non-fun. Needing more food does make some sense, and weighing as much as the rest of the party put together could pose problems for travel logistics (horses, polymorph to giant eagle) \$\endgroup\$ Mar 13, 2022 at 15:35

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