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Booming Blade is a fascinating cantrip. Between somewhat murky language and unclear use-cases, there's a lot of confusion among the 5e community about how exactly you're supposed to use the Asmodeus-blasted spell.

Booming Blade's description reads as follows:

As part of the action used to cast this spell, you must make a melee attack with a weapon against one creature within the spell's range, otherwise the spell fails. On a hit, the target suffers the attack's normal effects, and it becomes sheathed in booming energy until the start of your next turn. If the target willingly moves before then, it immediately takes 1d8 thunder damage, and the spell ends.

Most of the confusion about its use cases stems from the following fact: if you're in range to use the cantrip on an enemy, then they're in range to hit you, so why would they ever move from their position, thereby triggering the damage? This leads to all kinds of theory-crafting on how to force target of the spell to move, which inevitably leads to strategies that are either too difficult or too costly (in terms of action economy or combat resources) to be practical.

So, how can a player effectively use Booming Blade in combat?

In order to narrow down potential answers and prevent opinion-based responses, the following criteria define "effective use" of Booming Blade:

  1. The cantrip is used in a way that guarantees one of the following:
    • The target suffers the secondary portion of the damage.
    • The player is able to influence the battlefield in such a way that increases their odds of success in some way that does not involve directly dealing damage via the cantrip; e.g. forcing the enemy to move into a desirable location.
  2. The usage of the cantrip is "economically efficient" with respects to action-economy; i.e. the player is not reducing their effectiveness by choosing this Action over another.
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    \$\begingroup\$ Would you consider builds that utilize feats to be "effectively using" the cantrip? For example using Polearm Master and Spell Sniper \$\endgroup\$
    – Medix2
    Jun 12 '20 at 3:20
  • \$\begingroup\$ @Medix2 absolutely. I do consider those opportunity costs but just about any strategy requires some kind of optimization \$\endgroup\$
    – Andrendire
    Jun 12 '20 at 4:20
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    \$\begingroup\$ Should we consider, that after lvl 5, Booming Blade also grants 1d8 (2d8-3d8) extra damage to the attack when it hits, not just when the target moves? \$\endgroup\$
    – IanDrash
    Jun 12 '20 at 13:54
  • \$\begingroup\$ @IanDrash yes that's a valid consideration, however I am interested in responses that focus on why you would choose this cantrip over another response that scales in the same way. \$\endgroup\$
    – Andrendire
    Jun 12 '20 at 23:11
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As a Readied Action

One of the problems that melee combatants face once they get Extra Attack is that Extra Attack is only usable on your turn. As such you cannot use Extra Attack as a readied action. What you can do, however, is ready Booming Blade and take advantage of the extra attack damage at higher levels.

To encourage the enemy to deal with you

If you are a frontline fighter (such as an eldritch knight, Hexblade bladelock, high elf barbarian) you might prefer the enemy attack you rather than go around you and attack the squishy caster in back. Depending on your build you might do more damage with an extra attack than with Booming Blade even if the target moves. What Booming Blade offers, however, is a way to incentivize the enemy to stay put. Sometimes even a regular wizard/sorcerer/warlock might want to be a substitute tank if they managed to avoid damage in earlier combats and the regular tank is low on health.

To prevent the enemy from fleeing/disengaging

There are many enemies that can retreat without provoking opportunity attacks. This can be especially inconvenient if you cannot just follow them (they can fly, they are faster than you). Booming Blade help keep them nearby so that you can attack them next round.

To harm the enemy if it follows you

This is especially applicable for Arcane Tricksters who can Booming Blade and then disengage but it can be also helpful for someone who is willing to risk an opportunity attack to keep the enemy from following. For example you are a warlock facing a bandit. You could disengage but the bandit will just follow you. You could dash but so can the bandit so you will end up in the same situation. But if you booming blade and then retreat and the bandit stays put you can then dash on the next turn and the bandit will be unable to catch up.

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Many enemies do not want to be in melee

There are a lot of enemies who are fragile, magic casters, sneaky, or ranged fighters. They would love to run and hide if you get into combat. Booming Blade deals extra damage if these targets run, so it can help you control the fight by forcing them to take extra damage, or stay in an unfavourable situation.

Fighting packs of goblins at low levels illustrates this problem. When a goblin gets hurt at all, the cowardly creature is likely to flee or at least try and put distance between themselves and the PC so they can hide and use ranged attacks. Using Booming Blade makes running a less appealing choice, so they are forced to stay and fight and can be easily dispatched.

I have found that Arcane Trickster in particular can make effective use of Booming Blade. An enemy force consisting of tanks, and back liners is vulnerable to rogues. Rogues can easily flank the back liners and take them out with heavy damage. Enemy back-liners can always choose to run away (maybe disengaging) against a normal rogue, but ATs have familiars and Booming Blade, so if you run away then you can expect Booming Blade damage and a sneak opportunity attack.

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The Mobile Feat

This is a perfect use-case for picking up the Mobile feat. It has three attributes to it, but the primary one we care about here is the third one:

  • When you make a melee attack against a creature, you don't provoke opportunity attacks from that creature for the rest of the turn, whether you hit or not.

This is similar to the Fancy Footwork feature of the Swashbuckler Rogue. It allows you to freely disengage from an enemy after an attack, regardless of whether you hit or not. Mobile also grants an extra 10ft of movement, giving you more versatility in approaching, attacking, then putting distance between yourself and the target.

When combined with Booming Blade, this means you can get a free disengage after the attack, forcing the creature to either take the damage, or else be limited in its options the following turn. Mobile has good general-use buffs that synergize well with most classes and requires no additional actions (and in some cases such as Rogues and Monks, can save them their bonus action by giving free disengage from the target), meaning the opportunity cost is minimal.

I've used the Booming Blade/Mobile combo on both a Bladesinger Wizard and an Arcane Trickster Rogue, and both were able to use the spell very effectively. Combined with a Druid party member who had Moonbeam, we were able to consistently force enemies to take damage whether or not they moved.

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    \$\begingroup\$ +1 this, but I'll add that the extra 10ft of movement from Mobile is particularly meaningful. I played an arcane trickster with Mobile and booming blade. Part of what made the combination so devastating against melee-heavy foes was that most were slower than my PC. There was essentially no way they could ever land a hit: they couldn't close to melee range without dashing. Then I'd nail them with booming blade, dart away, rinse, and repeat. Foes dumb enough to give chase went down quick, and the smarter ones simply gave up and fled. \$\endgroup\$
    – screamline
    Jun 12 '20 at 20:04
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You cannot guarantee the extra damage (there are no guarantees in life). It's a risk like everything else.

So why use it?

Because it potential extra damage

This spell is the domain of Sorcerers, Warlocks, Wizards. These classes do not have a natural Extra Attack in a round 1. Meaning that when they attack with a weapon, they only get one shot. So adding a little extra potential damage is not a bad thing. Also remember, beyond the early levels, it does add extra damage no matter what. Moving just adds to it.

It's just a cantrip

Since it's a cantrip, you can cast this every round and also team it up with any of the bonus action "Smite" spells for even more damage for the initial attack.

Tanks

It's great for "tanking" type characters.

Picture an enemy that wants to get at someone in the back. One hit from you and now they have a serious choice to make:

  • Keep moving and suffer the extra damage
  • Stay put and face the attacker

It's similar to the Sentinel feat that forces someone to stop moving. It is for battlefield control.

1 There are ways to get Wizard cantrips through race, subclass, domain, and such. So this may not apply to everyone, but it's a good general consideration.

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    \$\begingroup\$ Cantrips are available to everyone through the magic initiate feat. Any Human can get this right from the start regardless of class. \$\endgroup\$
    – JDM7
    Jun 12 '20 at 8:28
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    \$\begingroup\$ @JDM7: Any variant human, but yes. :P \$\endgroup\$
    – V2Blast
    Sep 4 '20 at 9:03
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Booming Blade is not a cantrip for full casters; if you are in melee range you are probably trying to get out of melee range, not do a bit of extra damage. It's also not a great choice for Arcane Knights at higher levels, since you'll be forsaking extra attacks in order to do an extra few d8s of damage, maybe. However, a few situations where Booming Blade could shine:

When your melee attacks outrange your melee opponent and you have spell sniper.

Hit with your whip, and they still need to move to claw you. That's free damage!

When you are a single-attack melee character wanting to add some damage.

This works for a rogue or cleric with magic initiate/high elf magic/a dip into Sorcerer or Wizard.

When you can easily disengage

This works for a swashbuckler or any character with the Mobile feat; alternatively, a rogue willing to spend their bonus action on a disengage Cunning Action. At higher levels, booming blade + sneak attack could be a lot of dice to roll ...

DISCLAIMER: Most of these use cases are for roguely types; when you use a cantrip to make an attack, you are not using the attack action and, per PHB 195, you can't use a second weapon. This means that you only have one chance to make your sneak attack, which can be a questionable gamble for a 1-3 d8s of damage.

When you want to control the battlefield

5e has no taunt mechanic, so any ability that discourages monsters from pouncing on your squishy Warlock or your concentrating Cleric is worth considering.

DISCLAIMER Most of the classes that are able to take a hit will be forsaking multiattacks to use Booming Blade, which diminishes its utility significantly.

Anyways, at one point, I spent a lot of time theorycrafting a character that uses Booming Blade, but when I took my high-elf swashbuckler to the table, I found that it was much less risky to get extra damage by dual wielding, assuming that there was a significant chance that I miss on my first attack. The spell is highly situational, and I would advise you against building a character around it, though it does have uses!

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  • \$\begingroup\$ concerning your disclaimer: War Caster can solve that issue, as it allows you to cast Booming Blade instead of making an opportunity attack. OAs don't benefit from extra attack anyway, so it's basically free damage (except for the feat required, but that's not an issue for a semi-high-level high elf fighter who took Booming Blade as his racial cantrip and gets tons of ASIs in order to grab the feat). Same thing goes for a rogue, but a rogue likely doesn't want to tank that much. \$\endgroup\$ Jun 24 '20 at 23:05
  • \$\begingroup\$ They are apparently going to change the range in Tasha's, so you may want to be prepared to update this fine answer when that new version of BB comes out. \$\endgroup\$ Nov 6 '20 at 14:43
  • \$\begingroup\$ Isn't booming blade already limited to 5 ft? If so you can't use it to outrange enemies. \$\endgroup\$
    – Dezvul
    Nov 9 '20 at 7:10
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Why Booming Blade may be beneficial for typical "melee" classes, too

It seems to me that one can classify the possibilities, how to use Booming Blade effectively within combat, into two categories. The first type regards the ways to make use of the damage that takes/would take effect when the enemy willingly moves and multiple approaches have been discussed within other answers on this site. Therefore, I will focus on the second type: Ways and situations in which one can take advantage of the on-hit additional damage that Booming Blade deals starting from level 5:

At 5th level, the melee attack deals an extra 1d8 thunder damage to the target, and the damage the target takes for moving increases to 2d8. Both damage rolls increase by 1d8 at 11th level and 17th level. (XGE/SCAG, emphasis mine)

As it has already been noted, this improves melee attacks for primary spellcaster classes such as Sorcerer and Wizard. However, with one of these classes you probably want to avoid getting into melee range anyway and this limits the use of Booming Blade. So how do we use the Booming Blade on-hit effect effectively as a Barbarian, Fighter, Monk, Paladin, Ranger, Warlock, etc.?1

Restricting effectiveness: Booming Blade vs. Extra Attack

Booming Blade clearly has no synergy with Extra Attack: On the one hand, using Extra Attack (e.g., from the Barbarian, Fighter, Monk, Paladin or Ranger class) requires to take the Attack action first (and the same holds for the Thirsting Blade Invocation from the Warlock). On the other hand, to use Booming Blade one takes the Cast a Spell action and then does a melee weapon attack (not an Attack action) within this action. So, for an action you have to choose one or the other, but not both. However, even the aforementioned classes can benefit from using Booming Blade - if they can anyhow get access to the spell - and here are ways that came to my mind:

Booming Blade helps keeping up with damage when Multiclassing

Features such as Extra Attack, Thirsting Blade or Improved Divine Smite come at a level (typically 5 or 11) that a character has in the respective class and they increase the damage dealt starting at these levels. Similarly, the damage of Booming Blade increases at levels 5 and 11, but these levels refer to the character level, i.e., the sum of levels that the character has in each of its classes. This does not make a difference, say, for a Paladin of level 5. But when multiclassing, this may make a world of difference!

Say, you're Warlock 3/Bard 2 or Paladin 3/Sorcerer 2. Then you cannot use the Warlock's Thirsting Blade or the Paladin's Extra Attack at least for 2 level-ups, while Booming Blade already does the 1d8 on-hit thunder damage in addition to your usual weapon attack damage. This difference becomes even larger the more you multiclass and allows you to benefit from low-level class features of multiple classes (in particular of those classes that are presumed to be front-loaded) while still keeping up with melee attack damage.

Booming Blade can do better mean damage at high levels (11+)

Excluding the Fighter, all (sub-)classes only get one use of Extra Attack within an Attack action, so assuming all attacks hit, the damage dealt during an action is twice the weapon's damage. On the other hand, Booming Blade deals the damage of one weapon attack plus 2d8/3d8 thunder damage (levels 11-16/levels 17-20) on a hit. So whenever this 2d8/3d8 is more damage than one weapon attack, the mean damage one does is better with Booming Blade.2

Say, you're level 17 (not Fighter nor Paladin) with the Extra Attack feature (or the Thirsting Blade Invocation), wielding a 1d8 magical (+2) weapon using a +5 damage (e.g., strength) modifier. Then (with a 5% crit chance) taking the Attack action as well as Extra Attack does 2*11.725=23.45 average damage (assuming a hit), while a hit with Booming Blade (including the chance to crit, but excluding the secondary effect!) does 25,9 average damage. On levels 11-16, however, this difference is less significant and probably even negative, depending on your damage (and crit) modifiers as well as your weapon.

Booming Blade increases the damage of opportunity attacks by using the Warcaster feat

If an enemy provokes an opportunity attack, you can use your reaction to make one melee attack against that enemy. Note that you don't take the Attack action, so Extra Attack does not apply to an opportunity attack. However, if you have the Warcaster feat, instead of making the usual melee opportunity attack, you can cast Booming Blade at that enemy using your reaction. Not only does this hinder the enemies movement by threatening the secondary damage of Booming Blade, but (as a character of level 5-10/11-16/17-20 and on a hit) this attack does 1d8/2d8/3d thunder damage in addition to the usual melee attack damage. That thunder damage is straight on top! Of course, the Warcaster feat is a costly investment, but if you can also benefit from its other advantages, it may be worth it.

Booming Blade adds a different damage type to your punch

Quite a few enemies have resistances, in particular against bludgeoning/piercing/slashing damage. So it can be very beneficial to circumvent these resistances by using the thunder damage of Booming Blade (a damage type seldom resisted throughout the Monster Manual).

Booming Blade works well with Smites/Crit-Fishing

Suppose you're a character that wants to add damage dice on a critical hit. You could be a Warlock who uses Eldrich Smite, a Paladin using Divine Smite or a College of Whispers-Bard using Words of Terror. In each of these cases, adding a damage dice comes with a fixed cost (e.g., the use of a spellslot or of Bardic Inspiration), while the benefit is doubled on a crit as each damage dice is rolled twice. Now if your chance of scoring a critical hit is low, it is probably beneficial to attack multiple times (using the Attack action and Extra Attack) to increase your chance to hit critically at least once (and then add those juicy additional dice). However, if your chance to crit is high enough to deplete your resources (spellslots, etc.) over the course of one day even by attacking only once per turn, then using Booming Blade clearly is beneficial as the on-hit damage of Booming Blade (1d8/2d8/3d8 at levels 5-10/11-16/17-20) is doubled on these crits. Unfortunately, there are many variables that determe the point from which on it is advantageous to use Booming Blade instead of the Attack action + Extra Attack (even more so since spellslots or Bardic Inspiration may be used for other purposes). Thus, one probably has to intuitively estimate within play whether to use Booming Blade or a normal Attack action + Extra Attack.


1 If a class does not provide Booming Blade as a cantrip (as it holds for most "melee" classes), one can access Booming Blade through the Magic Initiate Feat, by being a High Elf or by dipping into Sorcerer, Warlock, Wizard or Arcana Cleric.

2 If we're analysing the damage of a single-class Paladin, then one would need to compare 2d8/3d8 thunder damage with the damage from one weapon attack including the extra 1d8 radiant damage that Improved Divine Smite provides.

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Another potential synergy with Booming Blade is the war caster feat and Lightning Lure particularly on an eldritch knight. I like to call the combo "We're best friends now"

Application: walk up front for engagement too short of movement? Cast Lightning Lure to bring your new friend in for a lovely chat. They do not want to be with you - whack - use your reaction to cast Booming Blade via the War Caster feat. They now take extra damage as they move away from you. Depending on their speed you can easily follow them for simple attack actions, or, do the "We're best friends now" combo again if they have a higher speed.

Note: this starts to be even more effective at 7th level when eldritch knights have war magic allowing them to cast and then attack as a bonus action. It starts to plateau in raw damage in higher levels however.

This combination makes the player character keep a stronger control on the map by basically making one enemy be stuck on said PC, also the possible enemies trying to bomb rush past you for your allies backline. This makes it great for sword and board characters whom have high AC with shield spell. The only downside of the combo is that Lightning Lure is a Strength Saving throw which means if you want this to be effective then you do need a focus on Intelligence to ensure a harder DC.

The eldritch knight subclass Eldritch Strike feature says when you hit a creature with your weapon they have disadvantage on a spell you cast before the end of your next turn. This strengthens your grip on someone you pulled in with the "We're best friends now" combo since booming blade makes an attack in its casting. This means that even if you missed the Bonus Action attack from war magic you still have a chance to undercut the resistance for the Strength Saving throw of lightning lure via the reaction casted booming blade. Overall making it that much easier to solo someone out.

Another potential use of war caster feat is to cast Earth Tremor when someone is bomb rushing past you and your buddy seem to learn there is no escaping the magic of friendship. With Earth Tremor, especially if you are trying to attract everyone to you, all creatures in a 10 ft radius of you have to make a Dexterity Saving throw and take 1d6 bludgeoning damage (add a d6 per slot level above 1st) and knocked prone on fail or half as much damage on a save and dirt and stone become difficult terrain.

I find this to be an effective cast of the spell - when it's your turn again the enemies around you are knocked prone and you get that sweet buttery advantage. It even synergizes well with the Eldritch Strike feature since you can have two enemies make a saving throw with disadvantage when it comes on and possibly three the next level if you are going for a hey look at me play style via "We're Best Friends Now" combo.

For Roleplaying potential I like to think of it as a Bounty Hunter for having the great utility of controlling others movements to bring them in close warn them if they move or resist that they will have their body violently shake apart

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Take one of these feats:

  • Shield Master
  • Crusher
  • Telekinetic

Each of them allows you to move a creature either as a bonus action or when you hit it. This doesn't auto-trigger the damage (it has to willingly move) but if you push it out of its melee range, it will need to move to reengage.

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    \$\begingroup\$ Shield Master doesn't work as it requires taking the Attack action, and booming blade requires the Cast a Spell action. \$\endgroup\$
    – Someone_Evil
    Jan 23 at 16:26
  • \$\begingroup\$ On the other hand, Welcome to RPG.SE! Take the tour if you haven't already and see the help center or ask us here in the comments (use @ to ping someone) if you need more guidance. Good Luck and Happy Gaming! \$\endgroup\$
    – Someone_Evil
    Jan 23 at 16:27

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