the murder nerds

Today I’m looking at using dice beyond the usual platonic solids, and making use of strange wonderful things like the d7, d15 and d30.

Let’s face it, rolling dice is one of the best parts of D&D, and gaming in general (one of my friends uses a dice roller app – which is sick and wrong). Like most RPG gamers, I own a lot of dice, way more than is necessary. I sometimes make use of dice tower too, which seems to scratch an itch deep in my brain.

I recently received a bunch of weird dice from a project I Kickstarted. So I now have things like a d5, and d22! So what the heck shall I do with them?

The Stingiest Magic Item

One really simple idea is to just use the oddly-numbered dice for crappy ‘magic’ weapons.

Imagine your player’s emotions as you describe the properties of the ‘Sword of Nonagonia’: “When you hit with this ‘magical’ longsword, you roll a d9 for damage (or a d11 if wielded with two hands) adding your strength bonus as normal. Please note: this weapon does not overcome immunity to non-magical weapons.” What wondrous power!

I’m actually a little disappointed the dice arrived too late in my campaign. I would have loved to troll my group with this kind of loot. I mean, it would technically be the best weapon of its kind (maybe I could borrow a 3.5e term and call it ‘masterwork’), it would just be the most anti-climactic item to receive.

Attack Rolls with Big Dice

Ok, on to my real idea: I really like the idea of rolling a d25 or d30 for attacks. Like my wife tells me when we argue: “bigger is better”, so it would be cool to have the big boss of the dungeon roll a big d30 instead of a puny d20. But wouldn’t rolling a dice 50% larger break the game?

No! Well, not totally. Below is a graph of the probablity of hitting a certain AC, for a d20 with nothing added, a d20 with a +4, +5 and +6 attack bonus, and then a d30.

You can see that the attack bonus on a d20 roll just slides the graph to the right, increasing the chance of hitting any given AC (note that the probabilities only range between 5-95% because a 1 is always a miss and a 20 is always a hit). Hence a d20+4 has a 50% chance of making AC15, while d20+5 goes up to 55%, and so on. Meanwhile the d30 has a wider spread, making it equivalent to a d20+5 at AC16, but then having a slightly lower chance of hitting the lower ACs and conversely greater chance for higher ACs. Essentially a d30 has a greater ‘swing’, as you’re more likely to get a much smaller number (no attack bonus) AND a much larger one, as you’d expect.

So what does this mean for the game? It basically just reduces the importance of a character’s AC. The wizard wearing no armour has a slightly lower chance of getting hit, while the paladin with full plate is going to get hit more than usual. I think this works best for big all-or-nothing attacks where armour shouldn’t matter so much, like gunshots or a vampire bite. I was personally thinking of making use of it for my campaign’s boss, Helix, who has a laser beam day-ruiner weapon. I’d also say that it only crits on a natural 30, but in that case it does triple damage!

So in summary: rolling a d30 is roughly equivalent to 1d20+5, but with the effect of AC reduced. If you’re really worried this effect on your game’s balance, you probably shouldn’t do it; but if you just want an excuse to roll big stupid dice, go for it!

You could the same analysis for other dice sizes too: e.g. a d24 is about the same as 1d20+2. And you don’t need to limit this to only +5 (or +2) attack bonuses: 1d20+9 is about the same as 1d30+4, and so on. Although with larger attack bonuses, the lower hit chance for AC10-20 actually gives your players an advantage.