So there you are, facing off against the beholder at the end of an arduous dungeon. Your allies are dead or dying, and the monster has to be low on Hit Points.
If you can just survive this upcoming attack, you know you can take one last action and finally earn the perfect name for your sword.
The aberration turns towards you and glares with all nine of its quivering, unblinking eyes. It casts a spell.
You psych yourself up and start praying to the dice gods, let this attack roll low. But instead of picking up the d20, the DM reaches for a handful of d4’s.
This thing just casts Magic Missle, and all that’s left is to count the damage. You will die, and your party members’ deaths will have been in vain.
You still have a reaction, and because you are a smart, prepared player, you use that reaction to cast shield, negate the damage, and then take your turn to deliver the perfect one-liner:
“My sword’s name is Beauty, and it’s time to put it in the eye of the Beholder.”
That is, if you know what a reaction is and how to use it.
Reactions in D&D
In combat situations for 5th edition Dungeons and Dragons, Reactions are what allow you to do a little something extra in between your turns, such as provide one last escape when you’re staring down the barrel of a fireball or execute your clever stratagem at exactly The Right Moment.
When you’ve taken all of your actions, you still have one Reaction.
From the Basic Rules
Certain special abilities, spells, and situations allow you to take a special action called a reaction.
A reaction is an instant response to a trigger of some kind, which can occur on your turn or on someone else’s.
The opportunity attack, described later in this chapter, is the most common type of reaction. When you take a reaction, you can’t take another one until the start of your next turn.
If the reaction interrupts another creature’s turn, that creature can continue its turn right after the reaction.
As you can see, Reactions are a highly versatile tool in the order of combat, allowing you to act in the middle of another character’s turn.
A Reaction is always in response to a trigger.
Whether that trigger is specific to the feat, ability, or spell you are using or a trigger that you set before you take your action for that round, with proper planning you can make a game-changing move if you time it just right.
As stated above, the Opportunity Attack is the most common type of reaction.
The second is when you Ready an Action that you could normally only take on your turn and instead use that action to interrupt someone else’s turn, either to help an ally or hinder an enemy.
Let’s discuss these two common ways any character can use a reaction before delving into some specific feats, spells, and class abilities that allow you to take advantage of this precious space between your character’s turns.
Attack of Opportunity
As the Basic Rules state, the Attack of Opportunity is the most common reaction taken.
From the PHB:
You can make an opportunity attack when a hostile creature that you can see moves out of your reach.
To make the opportunity attack, you use your reaction to make one melee attack against the provoking creature. The attack occurs right before the creature leaves your reach.
Combat in Dungeons and Dragons punishes retreating by giving every character the ability to use their reaction to attack an enemy fleeing melee combat, provided the enemy did not use their entire action to prevent it via the Disengage maneuver.
If they do use the Disengage maneuver, you can not use your reaction to make an opportunity attack; however, they (probably) cannot do anything else with their turn.
You can take advantage of this mechanic by playing an aggressive melee character and focusing your attacks on a spellcaster or ranged combat specialist.
They will naturally want to create space to cast their spells or shoot their weapons.
By chasing them on your turn, you can force them into a stalemate where they cannot attack anyone but you and only with their touch spells.
If they want to affect the whole battlefield and protect their precious few hit points (which they do), they must continue running away from your overwhelming assault. A simple, yet satisfying strategy.
Ready An Action
Another technique available to all characters is the ability to ready an action. You can prepare any action that you would normally take on your turn and instead wait for the best moment.
To ready an action, you set a trigger anticipating what you think might happen and then tell the DM your intention.
If the trigger occurs, you can immediately take your action even if it interrupts someone or something else. The best way to learn this is by example.
Ragnar Brodelook is a crafty archer and brilliant strategist.
He has already seen the enemy cleric maintain concentration on a hold person spell to great effect against his friend Nocan the Barbarian, slowing him down so that poor Nocan can’t reach the cleric with his comically large sword.
Since Ragnar is a good friend and ally, on his turn, he will forgo making an attack and wait until his other ally, the wizard Lermin, casts flaming sphere and rolls it right up next to the enemy cleric.
Finally, on the cleric’s turn, they will move from behind cover to escape Lermin’s burning ball of napalm and Ragnar will use his reaction to finally release the shot he’s been holding.
The cleric will take the damage and will hopefully have his concentration broken, thus releasing Nocan from the hold person enchantment. Enter: the cleric’s sense of impending doom.
Ulrich is a Dwarven meat tank: tough, slow, and very dangerous over short distances.
He knows that he can be more effective on the battlefield if he can just get to the other side where all of the pesky spellcasters are. But they are 40 feet away, and Ulrich simply can’t cover it and attack.
But guess who can? His friend Loodittle the Druid can, provided he has wild shaped into his bear form! So they coordinate their actions.
First, Loodittle will use his bonus action to wild shape and then Ready an action to charge. Ulrich will use his move action to hop on Loodittle’s back and then Ready his action to attack.
Loodittle uses his reaction to charge, covering the distance to the spellcasters. Once there, Ulrich will use his reaction to attack the spellcasters.
It isn’t every day you see a rampaging bear coming your direction with a Dwarf on its back and a mean gleam in its eye. They call this technique the Ubear Driver.
Bildalf is a tricky little rogue with a handful of spells. He is being chased down a hallway by the town guard despite being completely innocent of any crime whatsoever. (Honest! Just ask his Mama.)
Yet, for some reason, this is not the first time he has been in this situation, and he is prepared for these shenanigans.
On his turn, he rounds a corner for his movement, hides as a bonus action, and then Readies a spell to cast. On the guard’s turn, they barrel right past Bildalf, and he uses his reaction to cast that spell.
He casts grease right under the guards feet. They slip and fall, thus losing the rest of their turn in a tangle of armored limbs and misfortune. This gives Bildalf a full extra turn in which to run away laughing.
Feats & Spells Which Use Reactions
There are many feats and spells which use reactions that range from the aggressive, the useful, and the life-saving.
Below is a table showing a number of feats and spells that utilize reactions. This list is not exhaustive by any means as new rule books are being published often.
Be sure to check the descriptions of feats and spells that sound interesting in order to take advantage of this fun mechanic.
Making the Most of Your Reaction
Finally, we will end with two character builds that make the most of reactions.
Build 1 – Inego, 5th level Human Fighter
Inego is a male human fighter who has dedicated himself to the study of the rapier so that he may avenge a murdered family member against a renowned duelist who is a member of the King’s Court.
Inego knows the only way he can defeat this evil man is to take him down in a sanctioned duel; however, he is not above taking the opportunity in a castle invasion should the circumstance arise.
Inego has three class abilities that allow him to use his reaction:
With Defensive Duelist and Parry, he can either negate a successful attack against him or reduce its damage. With Riposte, should an enemy miss with an attack, he can get an extra attack against them.
If you use Inego, consider multiclassing him with rogue in order to add Sneak Attack to his damage dice when he catches an opponent flat-footed.
Build 2 – Ballista, 5th level Warforged Rogue
The first thing Ballista remembers is gaining sentience while on a scouting mission for their employer, a Dwarf-owned mining company.
They were sent into a dark cave to reconnoiter the presence of kobolds in a potential dig site.
Armed with their crossbow, Ballista was about to take the perfect shot at a kobold worker when they had the thought, “Why?” come to them unbidden.
In that moment, Ballista realized they had no need for the money they were making, but instead were simply working as a means of fulfilling the emptiness inside of themselves where a sense of purpose belonged.
Ballista walked out of the cave, dropped their gear at their owner’s feet and declared that the claim of ownership was bestowed by the one who was owned and not by the one who claimed to own.
They have since wandered both the wild and the urban places, only working when they need materials for their body’s upkeep.
Ballista can use their reaction as a scout to move half their speed immediately after an enemy attempts to close into melee.
This maneuver should always be ready, so it would be good not to worry about finding a multitude of ways for Ballista to use their Reaction. Uncanny Dodge is a great back up for Ballista to use should they actually get hit.
If you use Ballista, consider multiclassing with an arcane spellcaster such as wizard or warlock.
This will allow them to take advantage of reaction spells should they manage to keep their distance or become the target of other ranged specialists.
Action economy is essential to effective combat encounters in Dungeons and Dragons, and it behooves you to never forget about the underestimated yet highly effective and versatile Reaction.