I like boss fights. They provide a nice change of pace from traditional dungeon exploration. Surviving their challenges and emerging triumphant. My Alexandrian Dark Souls setting will include a lot of boss fights, so I thought I'd lay out my general principles.
The Action Economy
I: Combat Effort
If fighting is sure to result in victory, then you must fight.
Five PCs can make five attacks in a turn. A standard enemy can only make one attack.-Sun Tzu
The obvious - and incorrect - adjustment is to make the one enemy's attacks five times stronger and give them five times as much HP. This can work, but it makes a fight deadly and boring. Damage isn't everything. The 5 "attacks" the PCs can make could include stun effects, terrain modification effects, confusion, flanking, pushing someone off a cliff, etc. Just multiplying the numbers won't help.
II: Bullshit Effort
If your enemy is secure at all points, be prepared for him. If he is in superior strength, evade him. If your opponent is temperamental, seek to irritate him. Pretend to be weak, that he may grow arrogant. If he is taking his ease, give him no rest. If his forces are united, separate them. Attack him where he is unprepared, appear where you are not expected.
Five PCs can get up to five times as much bullshit as a standard enemy. They can tie ropes, toss items around, communicate, plot, and execute. They can combine items, spells, and abilities.-Sun Tzu
The obvious adjustment is to give your enemy bullshit-cancelling techniques: stun effects, sleep effects, turning people into trees. These can work, but you can't cancel all bullshit all the time. Instead, bullshit right back.
III: Mental Effort
Be extremely subtle, even to the point of formlessness. Be extremely mysterious, even to the point of soundlessness. Thereby you can be the director of the opponent's fate.
-Sun TzuNo matter how clever you are, five players can still think faster than you because there are five of them. They might be thinking in different directions, they might be thinking incorrectly, they might be thinking themselves into trouble... but they are still moving faster than your poor GM brain can manage.
Good boss design can minimize mental effort. At a bare minimum, the boss fight should include all the information you need. If an enemy can teleport, don't list dimension door. List the range and limitations. Having to pause in the middle of a fight to look up some minor detail is a waste of everyone's time.
The Elements of a Boss FightYou don't need to include all these elements in the same boss fight. Pick and choose.
I: The RulesBosses can break them. End of story. A fair fight is a fight you've already lost. Your rules say enemies attack once per round? Screw it, this boss attacks three times around. Your rules say creatures have a to-hit value? Screw it. You can't hit this boss with conventional weapons, or you automatically hit them.
II: TerrainA 50'x50' room is boring. Consider including:
- Interactive (things to knock over, push, throw, or dodge)
- Intuitively connected areas (a room with a balcony, a sailing ship)
Unintuitively connected areas (portals, teleporters, floating platforms)
- Something going on (an active forge, a collapsing building, a rotating water wheel)
- Places to maneuver, hide, or circle around (pillars, darkness)
- Areas that limit movement (flowing water, video game lava or acid, swarms of slippery maggots)
- Dangerous areas (pits, drops, mashing gears, flame jets)
- Strong themes. This is almost mandatory. The arena should be as interesting as the boss.
III: PhasesTension in a boss fight tends to drop off fairly quickly. At first, there's this feeling of "Augh what the fuck is that thing!?", but players tend to figure out bosses fairly quickly. The fight becomes a slog.
You can continue to increase the tension by the uses of phases.
Phases can be triggered by:
- # of rounds since combat began (kill it quickly or it gets tougher or drag out combat to tire it out)
- Damage taken (1/2 HP or a specific threshold)
- Specific actions (melting ice, breaking chains, opening a door, using a spell)
- Phases can include:
- A change of boss moves (different or better attacks)
- An increase in the number of enemies (calling goblin assistants, splitting in half)
- An change in pace (slower or faster attacks)
A change in terrain (see above) as the boss moves or alters its environment
IV: Boss MovesA minimum starting point:
- One "moderate" damage attack. Enough to chip away at one or more PCs but not enough to kill a full health PC.
- One "oh fuck" damage attack. Enough to almost kill a PC or at least scare the hell out of your players.
- One "aha, thought you were being clever" attack. Usually an area-of-effect burst or a re-positioning.
- One "weird" effect. Passive or active. Does something unexpected. Helps control the fight, combat the PCs' bullshit.
- Telegraphed mega-damage attack. One round to get out of the way or you're probably dead.
- Area control attacks. Classic MMORPG boss fight moves. Designate an area; anyone in the area after a few rounds has something horrible happen to them.
- Reactions. Occur when a PC does something (casts a spell, fires a ranged weapon, smashes a vital gem). Breaks the normal turn order. Frightening.
- Summoning low-threat allies.
- Initiative penalties (this boss is really quick)
Multiple actions per round (It goes at the start of each round and in the middle of each round)
Actions after every PC's turn (It goes after every PC)
- Automatically hit (this boss is huge, you can't possibly miss) coupled with damage reduction (but it's so huge your weapons barely harm it)
Immunity to some types of attack
- An inconvenient movement move (flight, hovering, swimming)
- Immune until some action is taken (smashing a crystal, opening windows to let sunlight in)
- Terrain can be used against the boss (ancient rusting cannons on the balcony, fragile ceiling)
- A second boss arrives in the middle of the fight.
- The move's name and description should enable the GM to describe it, with as much or as little purple prose as needed, without preparing ahead of time.
- Powerful moves should be telegraphed. If a boss spits fire, its mouth should dribble flames all the time, even when it's not using that move. If it has a dart-forward multi-attack, it should move like a duelist, etc.
- Moves should be repeated to give the players a chance to learn and adapt.
- Try to include more than one path to victory. The Basilisk can be fought traditionally or blinded by stealth or fed to make it into a sort of ally.
- Some bosses deserve as much foreshadowing as you can give them. Hype them up. Give hints and warnings and, perhaps, mangled survivors.
- Some bosses should be horrible surprises.
- Not all bosses need to be larger or stranger than the PCs. The first boss fight in Bloodborne is against Father Gascoigne. He has the same equipment and the same moves as you... and he kicks your ass, because he uses them better. He thumbs his nose at the player. "I don't have any special advantages or tools. I'm just better. Get good, scruuuuub."
- Some bosses, especially ones with immunity to common attacks, can be treated more like puzzles than fights.
- Some boss fights can be tragic instead of hectic. They can be easier than expected for a reason that only becomes obvious later.
- A composite boss (a smaller creature riding a larger creature, two allies with different fighting styles, a caster and a sword-wielder)
VI: MusicBoss fights are a chance to get bombastic. If you don't use background music normally, now's your chance. Mostly silence, with only some areas having music, is a Dark Souls hallmark.
Your goal, as a GM, is to make the boss fight interesting. Take your time describing the boss and the terrain before the fight begins. Linger over details. Build a complete picture in your players' minds and you will be rewarded for it later.
Practice describing things. Go onto Artstation or some other site, find some monsters, and describe them - out loud if possible. Your goal is to produce an experience that your players will vividly remember.
Example Boss FightsThe Basilisk (by far the best and most complete boss fight I've written and tested)
The Stone Cobra Guardian
The Blizzard Eel
Xiximanter the Lich, the Apocalypse Shell, and the Umbral Duchess
Further ReadingHeld Kinetic Energy in Old School Arenas
JRPG Inspired Encounter Design
5th Edition's Legendary Actions
Action Economics 101 and 102
All the boss fights in Dark Souls
EDIT: Better Boss Fights