Which balancing issues, if any, would arise from allowing PCs to spend actions on bonus action features?

Question

I understand that RAW, features/spells/etc. that require a bonus action (e.g. Bardic Inspiration or Healing Word) cannot be used with a regular action instead (see this question).

However, what would be the long-term ramifications and effects on game balance if I were to instead allow PCs to use a regular action for bonus-action features/spells/etc.?

For the sake of narrowing this down a bit; I'm only asking about ramifications when allowing player characters to do this, no need to take NPCs or Monsters into account. I don't use the variant rule of feats either, so no need to consider those as well.

Answer 1

Doing so would massively increase the power of spells with bonus action control mechanics and create some other issues that utilize that feature.

Normally, the rules are very strict in that you only ever get one bonus action. If you were to convert that bonus action to an action, then there would be instances (Action Surge, Haste, etc.) that would then allow you to do this more than once.

The specific impact will be variable based on the specific bonus action under consideration, but changing it to a mechanic that would enable more than one could be very problematic.

I will review several interactions below that highlight the problem. The spellcasting actions are most problematic not because of being able to cast more than one spell (or not), but because many spells utilize the bonus action mechanic to control the spell. If you can use that mechanic twice, you are doubling the output of every spell that has that control mechanism.

Ready Action and Bonus Actions

Typically, you can not use a Bonus Action in a Ready Action. If you can convert your Bonus Action to Action, then it potentially works with this mechanic as well - giving further flexibility in how you use it and allowing for greater use/misuse of the secondary damage dealing that I cover later in this answer.

Bonus Action control mechanics and Bardic Inspiration* are two things that would benefit immensely from this

Bardic Inspiration

For instance, a Bard could now be able to hand out two Bardic Inspiration dice in one round. This doubles their current limit of one die.

Being able to hand out multiple instances of this limited resource could sway an encounter by boosting your party's effectiveness at twice the speed.

Spiritual Weapon/Heat Metal (or any other bonus action damage/attack mechanic)

Giving more than one Bonus Action here will allow multiple instances of damage delivery from these spells. If upcast, you could be looking at a max of 5d8+Modifier for spiritual weapon or 9d8 for Heat Metal. Any spell that allows a delivery of damage via bonus action would benefit and would become significantly overpowered as it doubles the damage output over the length of the spell (generally 10 rounds.) Especially if you compare that against other 9th level spells like Meteor Swarm. (Big Thanks to Axoren for this inclusion!)

To be clear, this is not casting the same spell twice, or overlapping effects. It is using the bonus action control aspect of these spells twice.

The damage output of spells that use bonus actions to damage would increase

In direct comparison, let's look at the damage outputs (assuming failed saves and successful attacks) for some of these to highlight the power of allowing two bonus actions to deliver damage from an ongoing spell/effect.

Meteor Storm as our Control example

Meteor Storm is one of the most powerful damage dealing spells available. I'm going to use the damage output from this as my measuring stick to compare against the effects of a dual bonus action mechanic.

Meteor Storm is an AOE, so it could effect as many creatures as you can fit within it, but each one would get a total of 40d6 damage. That's an average damage of 140 per creature in the range.

Spiritual Weapon

Spiritual Weapon is a single attack spell, but lasts for 1 minute with an average damage of 27.5 (assuming +5 modifier) being delivered twice for 55 damage per turn for a 550 total over duration. In order for Meteor Swarm to be outperform this, you'd need to get 3 targets which may be difficult to achieve.

Bigby's Hand

Bigby's Hand provides another OP option. In this case, the hand is much more versatile. It can be used via a bonus action to act as a controller (interposing itself between two creatures or shoving them) and as damage (Clenched Fist/grasping). Utilizing the single hand to have two potential targets alone is very powerful. If we look at the damage dealing for Clenched Fist, we have a delivery of 108 damage per turn or 1,080 over the duration. Meteor Storm would need to target 8 creatures in it's area in order to have a similar output.

Heat Metal

Heat Metal is only effective against someone wearing armor, but in this case it would deliver 81 fire damage per turn guaranteed. Meteor Swarm would have to target more than 10 to become equivalent.

Dual Bonus Actions are very powerful

While you may get 5+ targets in a Meteor Swarm attack, it's highly unlikely that they'd be arrayed in such a way and one of the most powerful spells in the book becomes dwarfed by many other options.

But the real kicker is you are now spending a minute dealing massive amounts of damage with only a single resource having been spent (especially for things that don't involve concentration where there is no risk of not completing the full minute.) The economy of doing that is overpowered.

Not only all of the above, but the one class ability where you could start to challenge the need for this is with the Potent Spellcasting. This class feature is a method for increasing the DPR of that specific class. If you do allow two bonus actions, thjen it completely negates the increase that Potent Spellcasting provides and greatly minimizes that level 8 class ability.

*^{Although Bardic Inspiration uses a limited resource, it shows that it removes limits on other features as well.}

Answer 2

Your rule change would make certain classes or builds more flexible.

With the rule as it is, players must be careful when building their characters, or choosing their spells, to avoid having lots of bonus-action abilities that can't be used together.

Example 1: Warlock.

Xanathar's Guide to Everything gives some new Eldritch Invocations and spells that activate with bonus actions:

• Maddening Hex Invocation (use a bonus action to cause damage to a creature you have cursed with the Hex spell, and its neighbours).
• Relentless Hex Invocation (use a bonus action to teleport next to a creature you have hexed).
• Crown of Stars 7th-Level Spell (use a bonus action to make one ranged attack, 4d12 radiant damage; the spell gives you seven of these attacks).

These are in addition to all the existing spells that are bonus-actions to cast and activate (I highlighted these because they are not affected by the one-spell-per-turn-except-a-cantrip rule). Currently, the player can only use one of these abilities a turn - they must carefully consider whether it is worth spending their precious Invocation / spell choices (warlocks can only learn a single seventh-level spell, ever) to get actions they can't use together. With your rule change, the player can safely choose as many bonus-action options as they want, without losing any flexibility.

Example 2: Healing and Area-Denial Spells for Druids.

1a. The bonus-action spell Healing Word heals 1d4+ability modifier hit-points, with a range of 60ft.

1b. The standard-action spell Cure Wounds heals by 1d8+ability modifier, but only at touch range.

2a. The spell Flaming Sphere is controlled (not cast) with a bonus action, and does (assuming failed save) 2d6 fire damage to one creature with that bonus action (it also damages nearby foes, but only at the end of their turns; they can easily move away).

2b. The spell Moonbeam is controlled with a standard action, but does more damage (2d10, assuming a failed save) of a more useful type (radiant) to more than one creature (5ft radius) at a more convenient time (the start of their turns so they cannot easily escape it; or if they try to move through the area) with an additional advantage against shapeshifters.

It seems that in both cases, the (a) option sacrifices raw power for flexibility, especially when the player's main action is still available for a weapon or cantrip attack. However with the existing rules, a player can't control their Flaming Sphere at the same time as casting Healing Word: the two "flexible" options aren't flexible together, and a player may prepare one of the (b) options instead (or as well as the two bonus-action options). With your change, preparing both (a) options is a very safe way to get maximum flexibility, and the (b) options are less inviting.

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Personal opinion time

You may think that these are extremely mild disadvantages to your house rule, and to be honest I agree. I think that flexibility vs. raw power is already an interesting choice when building a character, without worrying about "too much" bonus action versatility. But they are effects that will improve certain classes more than others, changing the game balance a little. Furthermore, you cannot simply declare "you can't do the same thing twice per turn" or similar caveat, as you could to limit the power of bonus-action spells; an increase in flexibility is almost unavoidable if you make the change.

Answer 3

Multiple bonus actions can stack and become overpowered.

Bonus actions usually do one of three things:

• Augment some action you can take "until the end of your next turn".
• Augment some action you can take this turn.
• Allow you to do something similar to a normal action after doing a certain thing for an action. (Example: two-weapon fighting.)
• Allow you to do something during a different character's turn "until the beginning of your next turn" without using a reaction.

Normal actions usually don't do these things, and if they do, it is to very measured extents. If you can augment your next action twice, the effects might stack or even multiply, causing an overpowered bonus. (That is the reason you can only have one bonus action per turn.) Same goes for doing something after a different character does something; for example, if you have the Tunnel Fighter feature

Tunnel Fighter (Unearthed Arcana): You excel at defending narrow passages, doorways, and other tight spaces. As a bonus action, you can enter a defensive stance that lasts until the start of your next turn. While in your defensive stance, you can make opportunity attacks without using your reaction, and you can use your reaction to make a melee attack against a creature that moves more than 5 feet while within your reach.

and another feature that lets you make spell attacks with oppurtunity attacks, like the War Caster feat, you can cast spells without spending actions or reactions.

Copying a normal action with a bonus action is also a problem. For example, if you have the Fighter feature "Action Surge"

Starting at second level, on your turn, you can take one additional action on top of your regular action and a possible bonus action. Once you use this feature, you must finish a short or long rest before you can use it again. Starting at 17th level, you can use it twice before a rest, but only once on the same turn.

and you can do a bonus action as an action, then you can probably find a way to stack the bonus actions while still using your action on that turn. Because bonus actions that augment same-turn actions are usually more powerful that those that augment the next turn(s), these two can potentially stack and create extremely powerful effects that are used on that same turn, which means opponents do not have time to react and counter you.

Answer 4

For long term effects on your game and the general balance, I think if you had players that began to commonly take advantage of this mechanic (i.e.-getting to double attack, double heal, etc.) then you would see the deterioration of those characters and the game. It would ultimately come down to if the players began to see it as "too good to pass up" and let go their previous aspirations for their character build just for the sake of a cool two-off.

I found this "master list of bonus actions and spells that can be used as such" that might be helpful for looking over and seeing exactly what people might be most tempted to try and take advantage of with that ruling. Overall, outside of aforementioned balance issues, the quality of the roleplay would be most at stake, in my humble opinion.

Answer 5

If you can limit it to only allowing it if the bonus action is spent on a DIFFERENT ability, this should be doable. This answers most of the concerns raised in the other answers, I believe.