A monster.

A spider with 4 legs. If you look closely, it looks like a tiny human being crawling on all fours, but with eight eyes in its face. If you listen closely, you can hear it singing ragged songs of bloody vengeance. Last year, they found the maiden, dead in the attic. The doctors said she got stung, but the wounds looked like miniature bites to you. And they just didn’t stop bleeding, even after she was buried. Everybody in town is still talking about it.

From the Tunnels into the Odd

… or how to convert Tunnels&Trolls monsters to Into the Odd.

Don’t get me wrong, I like T&T, I really do. But there’s so much math involved, it’s simply too much for me. It’s not complicated math, mind you, just basic addition and subtraction. But this is done every single combat round, and it usually involves high-ish two-digit numbers.

So how would I handle Into the Tunnels?
Taking a huge chunk from Chris Dowell’s guidelines, I’d say this:

Monster Rating

Look at the MR and divide it by 8. This gives you its D&D Hit Dice.
Does this make the monster…
… basic? Give it 1d6 hp
… survivable? Give it 2d6 hp
… majorly tough? Give it 3d6 hp
… life-threateningly dangerous? Give it 4d6, and cap out at 18hp.

Damage

d6 as a starting point
d8 for serious stuff
d10 for big stuff
d12 only for the biggest stuff
d20 for outrageously crazy shit

Special Attacks / Abilities

When a player character receives a Critical Hit (all hp are gone, and they fail their STR save), the monster‘s special abilities are activated. Don‘t wait for Special Attacks to be activated, though – they‘re always on. Use sensibly.

Diamond Lizard by David A. Ullery

So how does this hold up in real life?

Let’s take the Diamond Lizard (from Gristlegrim). To quote:

It lives in the deserts of western Rhalph and is a fierce predator. It attains a size of seven to nine feet in length and may be two or three feet in height on its wide-sprawling legs. It is as fierce and active as any wolf in the desert heat, but cold weather makes it go dormant and sluggish. The diamond lizard is renowned for the gemlike substance that forms and grows in its forehead–a jewel that looks very much like an uncut diamond. These jewels are prized as wand-stones–they seem to facilitate the casting of magic, and accomplished wizards can store spells within them along with the energy necessary to work those spells. The full grown lizard has a monster rating of 100 to 200.

Let’s go with MR 150. This translates to 18 HD in D&D. In ItO, this is definitely worth 18 hp. In T&T, the damage a monster potentially does depends on its Monster Rating: (MR/10+1)d6 +(MR/2). For the Diamond Lizard, we get 16d6+75. Just as comparison: In most T&T groups, an orc has roughly MR 20, resulting in 3d6+10. This lizard monster is about six times more dangerous than the average orc, so I’d give it at least a d10 damage.

The text doesn’t mention any special abilities, so let’s create one: When the Diamond Lizard does Critical Damage, it destroys one Oddity/Arcanum/Magic Item. Yes, it’s that bad.