Every good campaign needs a final boss fight, a dramatic climax of the adventure’s drama. Done well, the fight ties together weeks, months, or even years of play.
In this article, we’ll take a look at some ways you can design enemies and final encounters sure to offer a fair and memorable challenge to your players.
Watch the Action Economy
It is important to remember that the most precious resource in D&D is not hit points or spell slots, but rather the number of actions you can take. Even a 20th-level barbarian with 250 hit points will not stand a chance against a mob of foes all focused on him. Likewise, a party of adventurers all bearing down on a single creature (such as the final boss) are almost certain to overpower it.
The simplest way to balance the scales in the boss fight is to give the villain additional actions. Truly mighty creatures such as dragons and greater demons have these by way of the Legendary Action mechanic, which allows them to act throughout the round at the end of other creatures’ turns. However, the same thing can be achieved through providing allies for the villain, especially if they possess strategic abilities to bolster their leader, such as with shield guardians or any creature with Pack Tactics or a similar feature. A good rule of thumb is to have at least as many attack actions on the villain’s side as there are on the party’s side.
Cover the Villain’s Weaknesses
There is nothing quite so frustrating as having your mighty villain neutralized in the first round of the final battle when the wizard casts polymorph, or when the warlord can’t hurt the party because all of the characters are flying and he only has melee attacks, or when the party has two spellcasters with counterspell who effectively shut down the evil wizard’s entire arsenal of abilities.
As part of designing your villain, be aware of what they can’t do and make provisions for how they would deal with such a situation arising. If they can’t fly, perhaps they or their associates have a ranged weapon or a few potent ranged abilities. If they don’t have a large hit point pool, they’re likely to keep a few tough bodyguards around—possibly even a fanatically loyal champion able to offer a major challenge in their own right. Spellcasters generally have at least a few moderately talented apprentices around who can offer meaningful support.
And, of course, there are always legendary resistances just to make extra certain that a failed saving throw doesn’t end the battle too early.
Flavour, Flavour, Flavour
There’s nothing more anticlimactic than fighting your way through a band of orcs only to find their leader is just another orc without any new attacks, abilities, or even just some glitter to make him sparkle. Some extra hit points might make a difference on paper, and maybe it will pose a bit of a challenge to your players in the moment, but without more originality the fight will soon be forgotten. You needn’t come up with entirely new abilities; it is easy enough to adapt existing mechanics to empower your villains, and the Dungeon Master’s Guide offers helpful advice on how to adjust creature challenge rating when adding new abilities just to help you make sure the battle is properly scaled to still give your players a chance.
Some creatures are, of course, dramatic in their own right. One doesn’t routinely go into the woods and encounter a dragon, so when a dragon turns up in a fight it generally doesn’t need a lot of customization. However, that doesn’t mean a dragon fight is necessarily going to be interesting, especially if it happens in a big, featureless room where the only thing to do is race to throw dice at the other side until either the enemy breaks or you do. Location is an important aspect to flavouring an encounter, and the features of that location can be just as interesting as new creature abilities.
Even if the final showdown with the villain isn’t to avert some world-ending calamity, the fight needs to be different from every other fight in the campaign to that point. Whatever aces you’ve been holding in the design of the adventure, now is the time to play them. Throw curveballs, subvert expectations, exploit blind spots. Make the fight as unique as possible.
Sample Boss Fight: The Ritual of Ascension
The archpriest of a dead god has uncovered a ritual to resurrect his patron by using his own body as a vessel. By the time the party arrives, the process is already underway.
Setting. The ritual takes place in an ancient temple built on a mountainside at a point where the barrier between the Material Plane and the Shadowfell is weak. Centuries of rough sea winds have toppled much of the structure, leaving mostly a shell with some limited use of an upper level arcade overlooking the sanctuary where the ritual is taking place. Spells that produce concussive effects such as thunderwave or fireball can destroy sections of the wall in their area of effect if they deal at least 25 points of damage.
Enemies. In addition to the archpriest (a chaotic evil war priest), there is the captain of the Black Templars (a neutral evil champion), seven Black Templar veterans, and three priests. The veterans are spread out, with two on the second level on each side of the sanctuary and the remaining three accompanying their captain in the sanctuary itself.
Protective Wards. The three priests are each wearing glowing amulets that are the foci for a series of wards guarding the archpriest. Maintaining the wards uses the priests’ concentration, but they can still cast spells using their actions. If their concentration is broken on the wards, they can resume it by taking an action to do so on their turn. The protective wards have the following effects, which are cumulative.
One priest concentrating. The archpriest has advantage on his spellcasting ability check to advance the ritual by one stage. Half of any damage the archpriest takes (rounded up) is transferred to the priest. If more than one priest is concentrating, the damage is divided equally amongst them.
Two priests concentrating. The archpriest has advantage on all ability checks and saving throws and gains resistance to damage from spells.
Three priests concentrating. The archpriest is immune to spells of 4th level or lower unless it wishes to be affected and is treated as under the effect of the sanctuary spell (save DC 17).
The Ritual. The archpriest may use an action on his turn to make a DC 12 spellcasting ability check to advance the ritual one stage. Maintaining the ritual requires his concentration and it fails if his concentration is lost. If the result of his check fails the DC by 5 or more, the ritual loses one stage of progress. If the result of his check exceeds the DC by 5 or more, the archpriest may immediately cast a prepared spell. The ritual succeeds when 5 stages have been completed. The ritual begins with 2 stages complete and automatically fails if it would be reduced below stage 1, or if stage 5 has not been completed within 10 rounds of the characters’ arrival.
Putting It All Together
Campaigns should end with a bang, and one of the best ways to do that is with an amazing boss fight. This can require preparation and foresight, as well as some exercise of your creative chops. By taking care to ensure your villain presents a new challenge to the party, you’ll ensure a memorable sendoff for the adventure.