Scalable Monster Statblocks For OSR Games

I've been thinking while working my way through the AD&D monster manual about how many monsters I would use if only they were lower in power. Obviously one can easily scale the monster down to a more reasonable level, but I wondered what a scalable statblock would look like.

Armor class could remain fairly constant, if you are assuming a low level system/setting, with a bounded armor class, so that wouldn't need to scale. The main things that would need to scale would be hit dice and attacks/damage, which you could decide to link together.

For scaling hit dice, I will use the notation "L" to represent the dungeon level. So a monster's hit dice could be written as L+1, indicating that their hit dice are equal to the dungeon level plus 1. Thus, a monster of that type encountered on the 3rd dungeon level would have 4 hit dice. This can also work in reverse, with a monster have L-2 hit dice. A monster whose hit dice would be considered 0 actually has 1/2 of a hit die, and a monster with hit dice in the negatives is treated as having a single hit point.

As a general rule when designing monsters, I give them 1 attack for ever 2 hit dice they have, rounding up. So a monster with 3 hit dice would get 2 attacks, and a 5 hit dice monster would get 3 attacks. If using this system, one could simply write down how much damage a monster does, and have attacks be dependent on hit dice.

Special attacks are more difficult, but you could use the simple route of dragon breath's damage, having special attacks deal damage equal to the monster's current hit points.

So, as an example, here is a scalable statblock for a giant black widow spider

Credit to DeanSpencerArt on deviantart

Giant Black Widow

# Appearing: 1

Hit Dice: L+2

Armor Class: 14 (medium)

Damage: 1d6

Movement: Average

Special Attack: The Giant Black Widow can choose to bite as one of its attacks, requiring the target to make a CON challenge roll or take damage equal to the Black Widow's current hit points. A successful roll halves the damage taken.

Sorry for the kind of rambling post, I just got off work and HAD to write this down.