I’m a big fan of games like Dark Souls or Monster Hunter. And one of the memorable aspects of these games are the fights against giant boss monsters. Monsters that can oneshot you, fights that you have to prepare for, forge special equipment, brew special potions and blade oil, study your opponent, learn all of their attack patterns and every weakness you can exploit.

You’re standard old school monsters and combat just does not have this depth. Beyond a large pool of hitpoints and maybe some special attacks, there is not much mechanical depth to even a dragon or a beholder. A good DM can improvise all of these aspects. If the player says, “I go for they eyes” you can say, sure, Attack with disadvantage, and if you hit the creature is blinded for d6 turns.But to make the fights truly memorable, and raise them to a major plot point rather than a random encounter, I worked out some houserules for my boss monsters. And I call them Kaiju, just to make it clear that they are a special kind of monster.

Kaiju

Kaiju are monsters that are stronger and scarier than any other. A true bossfight that cannot be overcome by strength of arms alone. They can be of truly titanic size, but they don’t have to be. A bear sized Waldschraat can be a Kaiju, if it confirms to these principles.

1. Kaiju are extremely powerful, they can only be overcome by careful preparation and clever fighting.
2. Kaiju have unique strength and attacks that can be learned, prepared for and defended against.
3. Kaiju have unique weaknesses that can be exploited to defeat them. 

The strength and weaknesses you can prepare for, are also how adventures involving Kaiju work. The death and destruction caused by a Kaiju can be the reason to hunt it, as could be the rare material you could butcher from it. Finding the tracks, learning the strength and weaknesses, preparing the weapons, potions, poisons and strategy are the body of the adventure, and the confrontation is the natural climax and boss fight.

To make my Kaiju as useful as possible to run an adventure like that, I prepare the following information:

Name

Kaiju are mysterious creatures; hardly any have ever seen them, but those that have witnessed them give them a name that is only uttered in fearful whispers. 

Tracks

The first sign of trouble are the tracks, destruction, and traumatized survivors left behind after a Kaiju attack. They give you the first glance at the size and destructive power of the creature, but should be open to interpretation, so the players can imagine a monster even scarier.  

Sound

The unique sound a creature makes as it moves is often the first warning you get of it; the sound it makes as it attacks is often the last.

Smell

The smell lingers in an area even after a monster is gone.

If your game involves a lot of dungeon crawling, sound and smell are also important because that will be all you perceive of a monster when your torch has died. 

Appearance

You only get an objective description of what the Kaiju looks like after you slay it, if at all. Focus on the impression it gives, the sublime feelings of awe and dread it invokes. 

Demeanor

Tells you what the creature will usually do, how it will act. 

Background

Where did the creature come from?

Motivation

What does the creature want?

Secret

Nothing is ever as it first appears, especially not Kaiju. 

Material  

What you can harvest from the creature, should you manage to bring it down. 

Stats

This is where we have the hard rules.

Armor Class, Hit Points, Movement, Strength, Dexterity, Constitution, Intelligence, Wisdom, Charisma, Alignment, Level.

Kaijus often have several body parts that can be attacked separately each with their own AC and HP, each with an effect when they are destroyed at 0 HP. Finding out where to hit a Kaiju with what attacks is one of the major challenges when fighting them.

The eyes are often a weak spot on a monster, unless they have like six of them. Give them like AC 20, 5 HP, and the monster is blinded if you destroy all of them.

Certain body parts can be associated with a certain attack, like the tail of a giant scorpion with the poisonous stinger. Destroy it, and the monster loses that attack.

Other parts might be for movement, shred the wings, cripple the legs, slow it down so it can’t run away. 

Rule of thumb, if your monster can do something really troublesome, there should be a bodypart associated with that ability. 

Attacking a specific bodypart often involves positioning, timing or attacking with disadvantage to hit them. 

Attacks

Each Kaiju has a number of signature attacks. Roll a die to randomly pick one, or have it do the attack that makes the most sense at any given moment. I usually prepare a d6 table of special attacks for this. Most of these attacks hit automatically, requiring a saving throw to avoid. AC alone won’t save you from a Kaiju. 

Weakness

A Kaiju is overwhelmingly strong from its pure stats. But each Kaiju has unique weaknesses that can be exploited to defeat it. 

So this theory is fine and good, but let me give you an example of what a Kaiju can look like, and how you use it to run an adventure. 

Example: Dracheneber

Tracks

Scattared, gnawed remains of burned wolves, black smoldering furrows in burned fields, crushed and burned farmsteads 

Sound

crackling wood, deep throated snorts, trampling of massive hooves 

Smell

charcoal and bacon

Appearance

A giant boar the size of a cabin, nostrils smoking, visible glow between the ribs, like a furnace burns in its chest, eyes glowing like hot embers, long black curving tusks, black spikes growing from its back

Demeanor

rummaging for food, defending its territory, this forest and all the surrounding land are his domain and he wants everyone to know it 

Background

A boar that has eaten the heart of fire elemental that fell from the stars 

Motivation

Hunger, defending its territory

Secret 

Other animals avoid it, which makes it impossible to find a herd, it’s growing desperate for company 

Material  

black tusks and spikes hard and fire resistant, thick fire resistant skin, 500 rations of hot smoking pork, the heart of a fire-elemental 

Stats

4 legs: AC 15, 10 HP, if one leg it destroyed the Dragoneber’s movement is halved, if 2 are destroyed its movement goes down to 5 feet, if all are destroyed it can no longer move or attack

2 Eye: AC 19, HP 5, if destroyed the Dragoneber attacks with disadvantage

Heart: AC 21, HP 5: If the heart is destroyed the fire elemental burst from the Dragoneber’s chest, killing it 

Tail: AC 14: HP 20, if destroyed the Eber looses its Tail Swipe attack 

Head: AC 15, HP 25, if cut off or destroyed the Eber dies and begins to roast

Body: AC 13, HP 50, If destroyed the Eber dies and starts to roast.

Any cut or pierced hole makes boiling blood sprout forth. An attacker in close must succeed with DEX 12 or take 1d6 dmg from the blood.

Immune to fire 

MV near, S +8, D +0, C +8, I -2, W -2, Ch -5, AL Neutral, LV 15

Attacks 

Weakness

A large quantity of water (10 slots of Equipment worth) can dose the Dragoneber’s flame for 1d4 rounds, until the water steams off it is drowsy and gets disadvantage on all actions and all fire dmg it might inflict gets reduced to 0. It’s as stupid as a normal boar but the fire within makes it far less aware of its surroundings.