Unfortunately the 2d10 has a drawback, each step isn't exactly separated by 5% chance of success or failure. This makes it complicated for GMs who are used to 5% steps to adjust probabilities.
The distribution for 2d10 compared to 1d20 looks like this:
|Roll||% 2d10||% 1d20|
It has a very low probability of rolling low numbers, 6% of rolling 4 or less compared to 20% on the d20, and similarly for values 17 or higher. This makes it a terrible option if you play games that require to hit a certain high value like some 18 or 19 armor value. It will be very hard for players to roll that high.
On the other hand 2d10 favors skill and adds predictability to the game. Lets change the rules a little and say a hit is achieved on a roll of 12 or higher. So our character fails on a roll of 11 or less, which is 55% for both 2d10 and 1d20. If the character enjoys a +1 modifier to hit, then an 11 is required and the odds of failing are equal to rolling a 10 or less. This amounts to 45% on 2d10 and 50% on d20. A skilled character has less probability of failing with 2d10, but this early benefit is offset by a slower progression later on. While the d20 continues to gran 5% benefits on every plus after +5 the 2d10 begins to give less and less for each plus. Meaning it becomes harder to get good the better the character already is. Which is, ironically, may be seen as a good thing. I certainly believe greater progression should have considerably greater cost. Don't you think?
So 2d10 has some really good benefits, like a non linear distribution that gives some predictability to the rolls and makes higher modifiers have less benefit. On the other hand it makes rolling a 20 an event one in one hundred, so forget about using it in classic d20 systems. It would simply mean a complete rewrite of all the combat mechanics.
So, as a player or GM have you played games that use such a roll? As a designer have you considered it as part of your mechanics? Yes, no, why? I make strong use of it in the combat and skill mechanics and would like to know what others think of this die roll.
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