D&D 5E Surprisingly, nothing breaks when switching D&D to 2d10 instead of d20

[NotAYakk]

Suppose you want to do 2d20 for ability scores, but don't have enough d10s.

You can just do 2x proficiency bonus for all ability checks, and ~3x for expertise. That'll get pretty close.

Or, add both your proficiency bonus and a proficiency die. Which is fun. Expertise roll the die twice and take the better result.

+2: 1d4
+3: 1d6
+4: 1d8
+5: 1d10
+6: 1d12

The "success and magnitude" that you sometimes want can also leverage this. If you need a magnitude of success, you can take proficiency die plus attribute bonus (min 1).

Int 16 profi +2 goes from +5 to +5+1d4, which is about 1.5x
Int 20 prof +4 goes from +9 to +9+1d8, again about 1.5x
Int 14 and +6 prof (expertise) from +8 to +8+2d6 1.6x
Int 20 and +12 prof (expertise) from +17 to +17 +2d12 drop lowest is about 1.5x.
Int 20 and +6 prof from +11 to +11+1d12 1.6x.

 

[GlassJaw]

Honestly, I like 2dX or dice pools systems better than d20 but you need a completely different modifier system and TN system.

 

[Horwath]

It makes critical hits much less likely, and thus nerfs crit-fisher builds.

so you put crit at 18-20(instead of 20 on d20, 6% chance) and 17-20(instead of 19-20 on d20, 10% chance) and 16-20(instead of 18-20 on d20, 15% chance)

have advantage be 3d10 drop lowest and elven accuracy 4d10 drop 2 lowest.
less attack bonus in numbers, but higher crit chance.

 

[ConflictGames]

how do we handle keen weapons improvements to criticals?

 

[NotAYakk]

so you put crit at 18-20(instead of 20 on d20, 6% chance) and 17-20(instead of 19-20 on d20, 10% chance) and 16-20(instead of 18-20 on d20, 15% chance)

I'd make it "any hit that is doubles" is a crit. That is about 10% of hits, which is about 5% of the time.

For extended crit range, I'd let you roll an extra crit-only die for each extension; if it matches the highest d10 you rolled, you get a crit (but only the highest).

Advantage, add an extra d10 to your roll, and pick any 2. Triple-advantage, roll 4d10 and pick 2.

So a 19-20 crit range with triple advantage is 4d10 and a 1d10 crit die. If you can arrange to hit so that the crit die matches the highest d10 rolled, you get a crit, or if you can hit with pairs. Makes it a little game of Yahtzee.

how do we handle keen weapons improvements to criticals?

There aren't keen weapons in 5e.

 

[Paul Farquhar]

so you put crit at 18-20(instead of 20 on d20, 6% chance) and 17-20(instead of 19-20 on d20, 10% chance) and 16-20(instead of 18-20 on d20, 15% chance)

have advantage be 3d10 drop lowest and elven accuracy 4d10 drop 2 lowest.
less attack bonus in numbers, but higher crit chance.

Sure, you can fix it. But the OP's claim that it breaks nothing is false. It actually breaks quite a lot of things, including the adage "if it aint broke don't try and fix it".

Off the top of my head, a list of some things that break:

Halflings: Lucky trait
Half orc: Savage Attacks trait
Barbarian: Brutal Critical
Champion: Improved Critical
Hexblade: Hexblade's Curse
Feats: Elven Accuracy, Great Weapon Master

 

[tetrasodium]

I'm sure that with a few edge cases (like the crits someone mentioned) that it would work fine. If you look back at 2e you had d20 & 2d10/d100 running side by side with d20+mods() for attacks & d100+mods for skills(which tended to scale in multiples of 5).
2e armors

2e thief skills

 

[Shiroiken]

It does upset the math, but as @NotAYakk excellently pointed out this can be corrected with some work. I think it works much better in ability checks than attack rolls and saving throws, as it would represent a more balanced result (easy things don't need a check, and hard things are actually HARD). Attacks and saves are supposed to be fairly swingy, however, representing a great deal of luck and randomness during the chaos of battle.

I'm not sure how much benefit one gets for the effort, assuming one wants to re-balance the math. It's probably easier to switch to proficiency dice, which has a similar effect, if to a much smaller extent.

 

[Charlaquin]

Since I've started using fixed DC (10- fail, 11-17 partial success, 18+ full success), I was playing around with various ways to shift the numbers to generate more partial successes on average, while still allowing +0 characters to achieve full success. The most radical solution I had in my list was to switch to 2d10, which I recently tested, just as a joke.

But, to my surprise, it worked. Like, worked very well. It breaks nothing, while seriously reducing σ.

I would argue that seriously reducing σ is breaking the game. The game was designed around the σ it has, reducing it is by definition breaking that design conceit. Now, that may be a desirable thing for you, in which case, awesome! I’m glad you found a way to achieve that without significant undesirable side-effects. But I don’t think it’s accurate to say nothing breaks. You’re literally breaking some of the most fundamental underlying assumptions of the game’s math. But if that improves the game experience for you, have fun!

 

[DEFCON 1]

Sure, you can fix it. But the OP's claim that it breaks nothing is false. It actually breaks quite a lot of things, including the adage "if it aint broke don't try and fix it".

Off the top of my head, a list of some things that break:

Halflings: Lucky trait
Half orc: Savage Attacks trait
Barbarian: Brutal Critical
Champion: Improved Critical
Hexblade: Hexblade's Curse
Feats: Elven Accuracy, Great Weapon Master

Depends on how you define "break" I guess.

If you use it to mean "doesn't work correctly as-is"... then sure, Lucky is "broken" because if you can't roll a 1 (since 2d10 is incapable of rolling 1s), you can't re-roll said 1 using Lucky.

But if you use "break" like I do, which is that the rule fundamentally breaks the game and makes it incapable of running correctly... then none of those things you wrote I would consider broken at all. Because it would be frightfully easy for me to re-write those abilities under the new 2d10 paradigm.

If you really want to get all verbally nitpicky because the OP used the word "nothing" then I suppose you can go ahead. But that's an unnecessary attempt at starting an argument if you ask me.