Solo Boss Encounters in D&D-Like TTRPGs

 Solo boss encounters are a common thing that people want to do in D&D-likes, but the way the system is set up, they don't really work unless you mess with it.

This post is a description of how I mess with it to make them work better.  It might not work at all for you or maybe it will be the most brilliant thing you've ever heard of.  These ideas aren't new but also it's the result of mashing together decades of blogs and different RPGs and trying things out so I don't remember what the sources are.

So:  Solo boss encounters.  We're defining this to mean a challenging, interesting battle against a single combatant.  There's lots of other ways to make a 'boss' encounter but I'm not talking about those here.  The most common thing people try to make this work is to just use a higher level monster; this has various issues depending on system, but most often, makes for a frustrating experience because its AC is too high, its saves are too good, its damage is too high, or more than one of these things.  Then the action economy doesn't let it actually do enough things to feel like an active fight, because these games aren't designed for a 1vX fight, they're designed for lots of things to be on the field on both sides, so it just stands there getting missed/making saves and then one-shotting people.  Tonberry is a boss fight, all right, but it's not really the one that people are looking for most of the time.

The trick I use is basically, just duct tape a bunch of monsters together and make it a single monster, then invert the action economy.

Duct taping them together is relatively understandable; just mash them all up as if the party was facing multiple monsters.  Inverting the action economy only takes a tiny bit more explanation.  If the party was actually facing multiple monsters (let's say five ogres), then the enemy team would start out with five actions per round and go down to one action per round as the party dealt damage.  This leads to a cleanup phase and an anti-climactic finish.  Inverting the action economy means that the solo monster starts with one action per round, and as it takes damage, this increases until it's up to five actions per round.

For crowd control effects, obviously those have impacts on the action economy, and the answer like most answer is based on thinking 'what if it was five separate monsters'.  For each unique CC effect that would prevent them from taking actions, they lose one turn.  If they're paralyzed, they lose one of their turns each round; a second paralysis effect does nothing.  If they're paralyzed and stunned, they lose two turns each round, but another paralysis or stun wouldn't make it any worse.  This makes AoE CC less valuable against the duct taped version than it would be against the individual monsters, but because this lines up with the desired villain fantasy, that's all right, and it allows for CC to be useful against the boss encounter without ruining it.

You could probably figure out how I'd do this from what's written here already, but let's make an example monster instead.  I'll use the Ogre (CR2) from D&D 5E as an example here because basically everyone knows how to read 5E statblocks and Ogre is an SRD monster.  I'll start by going through each stat and describing what the effect of duct taping a bunch of them together (five, specifically, in this case) has on that stat.

Armor Class:  Unchanged.  Five ogres each have the same AC as one ogre.
Hit Points:  Multiply by five; five ogres have five times as many hit points as one ogre.
Speed: Unchanged.  Five ogres can move more often than one ogre, but not further, so speed changes are covered by action economy changes instead of altering the speed.
Ability Scores: Unchanged.
Senses, Languages, CR: Unchanged.  However, for CR, of course when encounter building you should consider this to be a number of creatures equal to the number you duct taped together; five ogres is five CR 2 creatures.  This means that the XP value listed in the statblock should be multiplied.
Actions:  Unchanged.  Just like speed, five ogres can attack more often than one ogre, but they don't do any more damage.

And then the only change needed outside the statblock is initiative/action economy.  Check the number of hit points a single creature of this type has.  Each time the monster loses that many hit points, it gets to take another turn in the round.  One ogre has 59 hit points, so each time five ogres duct taped together loses 59 of its hit points, it gets to take another turn each round.  (The five combined have 295 hit points, which sounds like a lot but is exactly as many hit points as you'd have to chew through to kill five ogres.)  You can roll initiative for it multiple times if you want, but usually it's easier to assign fixed numbers that each turn occurs on; you can either count down or count up.  Ogres are slow, so we'll have this one count up; they take their first turn on initiative 5, second on 10, third on 15, fourth on 20, and fifth on 25.  It'll start out slow as the party expects, and then become blindingly fast and dangerous at the end.

Depending on the party and the monster, you might find that damage values are scaling fast enough that your monster isn't getting to access all of its turns because it's being blasted through HP lines.  If this is happening, optionally, you can give them a bonus immediate turn right when the line gets passed.  This is also a great time to do any sort of phase transition you might want to do; maybe the ogre lights its club on fire and the damage becomes fire when it gets up to taking three turns per round.

And that's all there is to it.  Here's the statblock.

Five Ogres Duct Taped Together
Large giant, chaotic evil
Armor Class 11 (hide armor)
Hit Points 295 (35d10 + 105)
Speed 40 ft

Initiative:  Five Ogres Duct Taped Together don't roll initiative; instead, they act at initiative 5.  Each time FODTT loses 59 hit points, they can take one more turn each round, at an initiative count 5 higher than their highest current value (5, 10, 15, etc, up to 25 when they are down to 59 hit points or less).  (If you rolled hit points for FODTT, this occurs each time they lose 1/5 of their maximum hit points.)

Str 19 (+4), Dex 8 (-1), Con 16 (+3), Int 5 (-3), Wis 7 (-2), Cha 7 (-2)

Senses Darkvision 60 ft, passive Perception 8
Challenge 2 (2,250 XP)

Actions
Greatclub.  Melee Weapon Attack:  +6 to hit, reach 5 ft, one target.  Hit:  2d8+4 bludgeoning damage.

• Javelin (Melee). Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: (2d6 + 4) piercing damage.
• Javelin (Ranged). Ranged Weapon Attack: +6 to hit, reach 30/120 ft., one target. Hit: (2d6 + 4) piercing damage.

Rules Fragment: Nightfall Tactics

 Today I had a thought and had to write it down, so here we are.  This is the design fragment of a tactical wargame using the basic core of the Nightfall Engine (from Against the Fall of Night).  Rules terms that are referenced, but not defined here, are the same as in Against the Fall of Night.

Nightfall Tactics

A wargame/SRPG/tactical game built off an extension of the Nightfall Engine.

Tactics Skill:  Your default Tactics Skill is equal to half your Combat Skill.  Tactics Skill is used as the basic resolution roll for this layer (for example, if you're determining the effect of your infantry attacking, you roll Tactics Skill instead of an attack roll).

Strategic Skill:  Your default Strategic Skill is equal to half your Mind.  Strategic Skill is used to determine starting setup, layout, limits of units you can command, and so on.  It would be tested to determine if you can successfully ambush someone, get to the high ground before combat starts, etc.

Units can be actively commanded, or just on your team.  The number of units you can actively command is determined by your Strategic Skill, but you can have as many units on your team as you can hire (see the note on Wealth and Economy later).  You can only use your Tactics Skill to benefit units that you’re actively commanding.  (Thus a character with very high Tactics Skill, but low Strategic Skill is a fantastic sergeant or lieutenant who commands a single unit; a character with high Strategic Skill but low Tactics Skill is still useful as a commander of a large number of units to prevent them from default-stats.)

Feats can increase or affect both Tactics Skill and Strategic Skill.  (For example, a feat Magical Tactics:  You can use your Magic Skill instead of Combat Skill to calculate your default Tactics Skill.)

Strategic Spells:  Big battlefield versions of magic.  They take 10 minutes to cast (which is 1 round at this combat scale) and require the support of a company of mages (60 people who each have Magic Skill +1 or higher).  (Optionally, a total Magic Skill of 60+ is required, so you could have ten 6th-level thaumaturges cast one, if you somehow have those available.)  Caster characters can learn strategic versions of spells that they know with a feat.

Strategic Techniques:  Combat techniques scaled up to battlefield scale.  Martial characters can learn strategic versions of combat techniques that they know with a feat, and then units they command can use those techniques.

Units would be designed like monsters, with levels, stats, and basic attack and defense techniques.  The commander stats can replace certain stats here (like the unit would have a Combat Skill of its own, but a commander can use their Tactics Skill in place of it).

Units have Cohesion and Health in place of Vitality/Wound.  Cohesion reflects their ability to keep it together, Health is how many of them are still alive.  Like AFN, melee attacks that are not defended against deal damage directly to Health, while those that are defended against attack Cohesion first.  Ranged attacks always deal damage to Cohesion first, unless their attack test is a modified 21+ and the attack was not defended against.  Undead, constructs, and other mindless/controlled troops have Cohesion -, because they never break Cohesion and need to be actually destroyed.  Cohesion is also the Morale rules; when a unit hits 0 Cohesion, they need to make a check of some kind to stay on the field or else they disperse.  Whatever the check is by default, it can be replaced with a Tactics Test if the unit is being actively commanded.

Initiative phases are Ranged, Cavalry, Infantry, Magic.  (Flying cavalry, as a special ability, get to act in the Ranged phase.)

Strategic spells can’t be cast if the unit has been attacked that round, though the mage unit can still use their normal techniques.  Only a character with Magic Skill +1 or higher can actively command a magic unit; they just use their default stats if you don’t have at least Magic Skill +1.

Economy:  For balancing units against each other, there is some form of economy.  Units cost Wealth.  You can only keep a number of units supplied with total Wealth cost equal to your Wealth.  Default Wealth cost is Level, double for cavalry, but specific units may be more or less expensive.  (Note that multiple people can combine their Wealth to supply an army.)  (Note:  This makes it difficult for normal players to bankroll an army, and right now I don’t care, integration can get figured out later.)

Units don’t use Attack Points, Defense Points, or Magic Points, because a round is 10 minutes long and they have a ton of all of those points.  Instead, every technique or spell they have is very situational with distinct strengths and weaknesses.  If the unit has something that’s always useful?  That’s their special ability, being generically useful.  Each technique can only be used a specific number of times per round, usually once unless specified otherwise.

Units normally can’t do things that would make them Vulnerable while in melee.  Unlike individual characters who get to choose that kind of thing, units just aren’t given the choice.  A successful Tactics Test can get them done, or units with – Cohesion can do so automatically.

Damage is generally the same thing as on personal scale.  Rough default is 1d6 + Combat Skill, reduced by Armor which is usually approximately equal to Level.  Aura for undead, constructs, and anti-magic units.  Cohesion/Health is roughly half what Vitality/Wound would be on personal scale; units die faster than heroes (but it’s rounded to even numbers to make things easier to track).  Like personal scale, units can be ogre-sized or giant-sized as well, which makes them terrifying.

Units have facing.  We’re making a square-based wargame because I’m a heretic.  A unit has three front squares, two flank squares, and three rear squares.  Attacks from a flank have slight advantage, attacks from the rear have high advantage.

Weapon triangles:  We’re adding weapon triangles based on weapon qualities.  Cunning, Brutal, Reach.  Brutal > Reach > Cunning > Brutal.  If you’re on the good side of the triangle, you have slight advantage.  If you’re on the bad side of the triangle, you have slight disadvantage.

Basic unit statblock:
Wealth Cost, Level
Combat Skill, Magic Skill
Armor, Aura
Cohesion, Health
Attack Techniques/Defense Techniques/Spells

Two example units.

Militia (Infantry)
Wealth Cost 1, Level 0
Combat Skill +0, Magic Skill +0
Armor 0, Aura 0
Cohesion 2, Health 2
Attack Techniques
Swarm – The militia make a melee attack.  1d20+0, 1d4 damage.  On a miss, the militia take 2 damage.

Spearfighters (Infantry, Reach)
Wealth Cost 1, Level 1
Combat Skill +1, Magic Skill +0
Armor 1, Aura 0
Cohesion 4, Health 4
Attack Techniques
Long Strike – The spearfighters attack a target one square away from one of their front squares.  1d20+1 to hit, 1d6+1 damage.  This technique cannot attack adjacent targets.
Defense Techniques
Brace – The spearfighters set their spears to defend.  If the attacker misses, they lose 1 Cohesion.