Stupid DM Tricks: Stupid-Easy Monster Math

I'm not trying to milk the "hey, I'm a new father" thing or anything, but daaaaamn! That plus moving plus wife starting a new job and a small amount of just being personally overwhelmed with all of that stuff and other things I haven't mentioned means I haven't had much time to post lately. I aim to fix that. Here goes.

My discovery of what I call "Stupid-Easy Monster Math" has its root in several places. First, what the fuck does HD 1+1 mean? Seriously! Second, I hate to-hit matrices because I tend to think they should be much, much easier. Looking up every fucking attack a monster makes on a cumbersome table is counter-intuitive and boring. I want quick math that makes things make sense. The third thing is Kevin Crawford's "Target 20" mechanic which I only just connected to this whole process and it made me decide that it's worthwhile writing this post. In the end, I ended up with a simple process that SERIOUSLY speeds up combat on my end.

Here's the gist of the junk I'm about to lay out: there's a super-simple mathematical equation you can use to figure out whether your monsters hit your PCs or not using a standard, old-fashioned descending AC system. You can skip ahead to that part if you don't want my intermediate rambling.

Your game is complex enough already,
who has time for attack matrices?
To the first root, what the fuck does HD 1+1 or 3+1 mean? The obvious answer is that you roll the appropriate number of HD and add the number of the plus. To some of us (me) this means add the plus to each die but really, is that sufficient to warrant additional notation? Clearly it doesn't. If the only difference between a 1 HD orc and a 1+1 HD hobgoblin is literally 1 fucking hp, then there's no significantly interesting mechanical variation from one to another. However, the to-hit matrices I'm about to complain about illuminate a difference that's not quite obvious from just looking at the HD expression. According to the to-hit matrices that I bother to pay attention to (OD&D, BX & BECMI), an HD "1+" creature is treated the same as a 2 HD creature. Thus, unless we start statting up monsters as 1+3 HD or other nonsense, then the "+1" really means "it's really a 1 HD creature, but it fights like a 2 HD creature;" in other words, it's 1 HD tough, but 2 HD dangerous. Now that orc and the hobgoblin are significantly, interestingly mechanically different and we know what the fuck HD 1+1 means!

Part two: the to hit matrix is cumbersome and irritating! I don't mind making players deal with it but, after all, I'm probably going to have to consult it more times for my monsters' attacks then they will ever have to for their PCs' attacks. Realistically, it will always always ALWAYS take me longer to look something up on a table than it does to do a simple math equation. When I learned to play D&D "correctly" it was with AD&D and the end of BECMI, so we were dealing with THAC0, so simple math like this is good for my brain. With this background, I looked at the to hit matrices that I reference (mentioned above) and looked for patterns. Lo and behold, a pattern was easy to see: a 1 HD creature hits an AC 0 at 19 (or, has a THAC0 of 19), a 2 HD creature (or, as illustrated above, 1+1) hits on an 18, 3 HD hits on 17 and so on. Duh. Easy. To my mind at that point, the number "19" was a sort of hinge point: using it, I could figure out what any creature would need to roll to hit any AC.

The third part is where Kevin Crawford's Target 20 system comes in. In that system, you roll a d20, add some stuff and if you hit a 20 or better, you did the thing. Since I had been hinging everything on the number 19 (the point at which a 1 HD monster hits an AC 0), what's keeping my system from matching Crawford's? Only one thing, really: all I needed to do was make the HD of the creature in question part of the equation.

Here's what I came up with:

d20 + (Monster's net HD) + (Target's AC) >= 20 

Bam. Done. Math simplified, life made easier. You no longer need charts and tables and other nonsense. Go play games and run them from just your scribbled notes and a rough sense of how tough monsters should be because you don't really need tables anymore.

Oh, shit.


Saving throws.

I guess there are still dragons to slay...