How to use a BX Combat Matrix for Everything

Beating an AC of “Hard”

I like devising things that plug into an existing “system” without undue modification. The Combat Matrix can be used for any test. Consider that the BX table simply presents 13 steps of difficulty which happen to be rated from 9 through -3. In practical terms tasks may be rated from Easy to Hard, and for simplicity, Test Numbers 9 through 0 present an adequate range of Check Roll values.

The AC Number is converted into a Test Number

Character’s Level

Test Number

9

8

7

6

5

4

3

2

1

0

-1

-2

-3

Difficulty

Easy

Hard

Normal Man

11

12

13

14

15

16

17

18

19

20

20

20

20

1st to 3rd

10

11

12

13

14

15

16

17

18

19

20

20

20

4th + Higher

8

9

10

11

12

13

14

15

16

17

18

19

20

In a simple scenario a Player whose character happens to be a 3rd Level Fighter wishes to climb a vine covered wall. The Game Master must pick a Test Number from 9 through 0 which represents the difficulty of this task. If the Game Master picks a 5, moving down on the chart to the 1st to 3rd row one finds a Check Roll of 14 is required, and the Player must roll 14 or better using a d20.

That’s it!

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GregMacKenzie

Greg MacKenzie is the author of the novella Seven Crows a Secret, the Fenris 2d6 role playing game, adventure modules Gloomland, and Wildwood, as well as countless other adventures.

6 thoughts on “How to use a BX Combat Matrix for Everything

  • July 9, 2017 at 16:53
    Permalink

    This is brilliant – I can’t believe I’ve never thought of this before. The great part is that because it’s based on the Basic combat matrix, it progresses by level, not class (though I suppose one could parse out the “4th + Higher” into levels 4-6, 7-9, 10-12, and 13-15).

    I suppose one might also allow attribute bonuses? Like STR bonus for climbing the vine or INT for doing something smart?

    Deftly done!

    Reply
    • July 10, 2017 at 15:45
      Permalink

      Glad you like it! The idea came out of our other little side project. How many times have I heard a player say “I leap through the open window” and had no way to admin that action/test easily. This table kind of solves that conundrum. I chose the matrix from the Basic Book and in that the classes attack numbers are the same at those low levels, 1-3 anyway, so yeah its kind of classless and needs expanding. Yeah, why not allow the ability bonus for context, like trying to read ancient runes, definitely an INT related test.

      Reply
  • July 9, 2017 at 22:15
    Permalink

    I like the basic idea, though I’d probably use every other column to determine difficulty rather than all of them. Label them easy, average, challenging, hard, daunting, impossible and you’ve pretty much got the full range covered.

    Reply
  • July 11, 2017 at 18:05
    Permalink

    This is brilliant. I don’t think this can be said enough. I could see this, coupled with a sort of ‘good at’ classification for a particular task, replacing most any skill check system that can be used with B/X.

    Reply
    • July 12, 2017 at 16:14
      Permalink

      Hi Frotz, thanks and yeah, we do kind of need something like this for those “I leap through the window” situations that we all hear as DMs. How hard is it to leap through that window? Now we have something to pin a number and a check roll on, and we already know the mechanic. 🙂

      Reply

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