Creating Monsters on the Fly with Swords & Wizardry White Box

Swords & Wizardry White Box is probably (actually) my favorite RPG System.
The White Box game that I use is White Box: Fantastic Medieval Adventure Game
The PDF is free and it is probably one of the most used White Box systems.

The reason why I love White Box is that I often run games on the fly with little to no prep and it goes smoothly. The major reason for this is how simple it is to create Monsters & NPCs.

This is the stat block for an Orc in White Box
Orc
Armor Class: 6 [13]
Hit Dice: 1
Attacks: Weapon
Special: None
Move: 12
HDE/XP: 1/15

Short and sweet how GMing on the fly needs to be. But what do you do when your players encounter monsters and NPCs that aren't in the book? What if the Player Characters encounter a two-headed and four-armed monster that stands around 10ft high while one head spits acid and the other can hypnotize (charm) Player Characters. We will call it a Nookum.

First I determine the Hit Dice (HD), which if you haven't played White Box, the HD determines the health (Hit Points), the Attack Bonus and Saving Throw of the monsters. It is also a good estimate of the monster's "level." The more HD the monster or NPC has the longer it will stay alive in combat, the easier it hits the Player Characters and the easier it can resist the Player Characters spells and other special abilities. Hit Dice is rolled by six-sided dice. So I want to give Nookum 3+1 HD. What this means you roll 3d6+1 to determine the Hit Points. This also means when Nookum attacks it gets a +3 to-hit. The attack bonus for Monsters and NPCs equal their HD. And then Nookum's Saving Throw score would be 16 (19-HD).

Nookum
Hit Dice: 3+1
Attacks: +3
Saving Throw: 16

Now that I have that I determine what the Armor Class will be. Now, I use ascending Armor Class so I don't include the descending Armor Class. With Nookum's height it makes the monster easier to hit but also it has four arms which could be useful when parrying attacks. So Nookum's Armor Class will be 14.

Nookum
Armor Class: 14
Hit Dice: 3+1
Attacks: +3
Saving Throw: 16

Now it is time to determine what kind of Attack and Damage the Monster does. In White Box Monsters and NPCs only get ONE Attack. They do not have multiple attacks like in Swords & Wizardry Complete. Also, damage is based on six-sided dice. There are four different damage types that I personally use: Weak 1d6-1 Average 1d6 Strong 1d6+1 Deadly 2d6. With Nookum's four arms I feel that it would have a flurry of blows that deals 1d6+1 damage.

Nookum
Armor Class: 14
Hit Dice: 3+1
Attacks: Flurry of Blows +3(1d6+1)
Saving Throw: 16

Movement is the next thing to determine and it is easy. Movement Rate is in increments of 3. 12 is average speed (human). Some monsters might even have two different Movement Rates. One for walking and one for flying/swimming/leaping/etc. Nookum will have an average Movement Rate of 12.

Nookum
Armor Class: 14
Hit Dice: 3+1
Attacks: Flurry of Blows +3(1d6+1)
Saving Throw: 16
Move: 12

The last thing to determine is any Special abilities the Monster or NPC might have. In this case Nookum has two abilities. Spit Acid and Charm. For special abilities that are spells that Magic-Users or Clerics can cast it is just best to name the Special Abilities and that it works like Spell ______. For Special Abilities such as Spit Acid I determine that the damage equals the Monster's HD-1 and Save for half damage. For Special Abilities that are not spells and are not damaging abilities state what it does if the Player Character fails their Saving Throw.

Nookum
Armor Class: 14
Hit Dice: 3+1
Attack: Flurry of Blows +3(1d6+1)
Saving Throw: 16
Move: 12
Special: Spit Acid for 2d6 damage or Save for half damage. Can cast Charm Person.

The one thing I do not do is the Hit Dice Equivalent (HDE) and XP in my personal games. A good way to determine Monster XP on the fly is the Monster's Hit Points x 10.

So there we have it. A way to create monsters and NPCs on the fly. I hope this is helpful and understandable for you!