Quick Guide to Making a Fun 5-Stage D&D Boss Battle

I've run quite a few boss battles in D&D 5e since I started playing it several years ago, and almost none of them were very memorable, or even fun. In a few, the boss died very quickly from one or two critical hits (probably a paladin, or maybe a spell attack); and in others, the battle lasted so long we were all exhausted, and the sweetness of the victory suffered from it. I've realized from playing some memorable boss battles in games like Legend of Zelda and Assassin's Creed: Origins that to be fun, a boss battle must have one very important thing: stages.

It's not enough for a boss battle to be hard. A boss battle needs to feel like a series of encounters all on its own, each of which challenge the players in different ways while still maintaining echoes of familiarity throughout. A player whose go-to strategy is spamming guiding bolts and polymorphing into a giant ape when their hit points are low should certainly be able to entertain that strategy at first, but a later stage of the boss fight should make that strategy impossible or unstrategic, giving them a chance to try something else. The concept of Mythic bosses introduced with 5e's Mythic Odysseys of Theros was a pretty good addition to bosses, since it essentially added one more boss fight back-to-back with the first one with a higher difficulty, but you can do better in your games. There should be more variety in approaches rather than just simply higher damage to deal with.

I could probably spend a whole article talking about adding things like traps, dangerous terrain, and making the boss a load-bearing one so you only have time to pick one thing from its hoard before everything collapses, but this "quick guide" is too long already. So below is a quick reference to make a basic boss battle mechanically, and you can do all the fleshing out yourself.

Stage 1: Amusement

"Ha! You dare challenge me in my own lair? You upstarts must be truly foolish. Minions, dispose of these intruders."

Encounter: The boss, out of range/sight, sends 3 low-challenge creatures per character. See "Encounter Building" in Xanathar's Guide to assign a 3:1 "Multiple Monsters" challenge to each of your characters. This encounter should be Medium or easier.

Stage 2: Confidence

"Pah. Useless minions. You weaklings want a fight? Fine. I'll deal with you myself."

Encounter: When the minions are all taken care of (one or two of them might flee after the others are dead), the boss appears and fights the PCs in person, but it does not use Legendary Actions or Lair Actions yet.

Stage 3: Annoyance

"Enough of this waste of my time! Lieutenants, finish off these interlopers, and do it quickly!"

Encounter: When the boss is reduced to 0 hit points, it runs or teleports out of reach or sight. It then sends 2 monsters to fight the PCs. The monsters should be weaker than the boss but should still constitute a Hard encounter.

Stage 4: Fury

"RAAGH! That DOES it! Do you know how valuable those lieutenants were?! You're going to pay for your insolence. Now you DIE!"

Encounter: When the lieutenants both die, the boss appears and fights the players in person, this time showing some visual indication (such as the lair shaking or something) that they are willing to use Legendary Actions and Lair Actions this time.

Stage 5: Desperation

"This is impossible... What ARE you?! How do such pitiful mortals wield such power? This cannot be the end of me! My will and power are absolute!"

Encounter: When the boss is reduced to 0 hit points, it turns into its Mythic form, refreshing one of its Legendary Resistances and using Mythic Actions.

If you try this formula out, let me know in the comments how it works for you!