Minimalist OSR: Target 18?

I talk about Target 20 a lot in this blog. [for this post, I'm assuming you are familiar with Target 20]. I really like it. 

A few weeks ago, someone (might have been John Stater, author of Blood & Treasure* - this game looks awesome!) mentioned to me they used 18 instead of 20. 

And, well, I like this one too.

First, THAC0. Target 18 is a bit off, although target 20 is not perfect either. Doesn't bother me. Fighters and monsters hit more often if you're using descending AC and this system, which is nice. But, overall, I prefer ascending AC these days, so this is not a primary concern.

Now, thief skills. Again, target 20 works well, but target 18 gives the 1st level thief 20% chance with this system. It is closer to the original values, and thieves deserve a boost.

Same for saves. If you're using a single save, which I prefer, 18 is closer to the original numbers. And anything much lower makes it too easy if you're adding your whole level to saves, as Target 20 does.

Finally, 18 is, by itself, a 15% chance. And this is almost the same as 1-in-6 chances. You can use this as an universal mechanic to do anything for PCs that have no skills.

Anyway, here is what I am using for OSR minimalist system. You should check it out - there is a draft in my public folder.

To do anything, roll 1d20, add your ability score modifier plus other modifiers (e.g., from class or race), with 18 or more signifying success. A “challenging” difficulty is assumed; the GM may set other difficulty number (DC) for particularly easy or hard task, as indicated in the table below.

Notice that a DC of 18 is similar to 1-in-6 chances or 15% chance, making it easy to convert tasks from other systems to this one (e.g., if you have 3-in-6 chances of getting lost, avoiding it is an “easy” check). 4-in-6 would be closer to DC 7 but I like the 6-10-14-18 progression. Maybe I change it to 4-7-10-14-18 to fit the x-in-6 pattern...

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