D20 Combat in MZ

じ☆ve冰风

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The D&D-style combat using a D20 (a twenty-sided die) is really quite brilliant. It is not too difficult to incorporate a D20-style combat with Attack Roll v.s. AC and Spell Attack v.s. Saving Throw directly into RPG Maker. This guide is written for MZ but should work equally well with MV, as both use Javascript. Using it in Ace will require some formula modifications, but my other tutorial should help with that: https://forums.rpgmakerweb.com/index.php?threads/a-guide-to-damage-formulas.145148/. Please note that this tutorial will assume some familiarity with D&D combat.

To use D20 damage formulas, we begin with a dice roll.
1dX = Math.randomInt(X)+1
YdX = Math.randomInt(X*Y) + 1
If you're calculating damage with a 3d6 (simulating rolling a six-sided die three times and adding up the total), the formula would thus be Math.randomInt(18) + 1.

Okay, now in D&D the "Ability Modifier" is obtained by subtracting 10 from the Ability Score, dividing it by 2, and rounding it down (known in programming as truncating or flooring): M = Math.Floor((A – 10)/2). Of course putting this into RPG Maker will do nothing as "A" and "M" mean nothing to RM so we have to convert it into something it can understand.

Our full formula is basically going to say, "Okay, if the target AC is less than or equal to a 1d20 roll + the attack modifier + half the user's level, then deal YdX + the attack modifier damage. Else, deal no damage."

Written out, then, here's our full formula:
b.def <= (Math.randomInt(20) + 1 + (Math.floor((mod – 10)/2)) + (Math.floor(a.level/2))) ? Math.random(X*Y) + 1 + (Math.floor((a.atk – 10)/2)) : 0;. Now we can break it down.

• b.def <= ... ? :
  
  
  
  • We're checking to see if the target's "defense" (AC) is less than or equal to what all the following math will compute to. In D&D, that's a necessary prerequisite to do any damage. The ? and : are part of the ternary operator construct. I recommend reading another tutorial of mine for some instruction on that, but it's basically a simplified if-else. https://forums.rpgmakerweb.com/index.php?threads/a-guide-to-damage-formulas.145148/
    
  
  
• (Math.randomInt(20) + 1
  
  
  
  • This just simulates a d20 roll.
    
  
  
• + (Math.floor((mod – 10)/2))
  
  
  
  • Now we add our attack modifier. For mod you can substitute generally a.atk or a.mat, or any parameter if you want to get more creative.
    
  
  
• + (Math.floor(a.level/2))
  
  
  
  • Here we add half the level, thus finishing our if-statement condition. Remember, floor is just a round-down.
    
  
  
• Math.random(X*Y) + 1 + (Math.floor((mod – 10)/2))
  
  
  
  • This is the central damage calculation - we do damage equal to a YdX roll, just like in D&D, and then add the attack modifier damage. Once again substitute whatever you like for mod, generally a.atk for physical attacks and a.mat for magical attacks.
    
  
  
• 0
  
  
  
  • If the formula could not meet or beat the target's AC, 0 damage is dealt, and it's a miss. Be sure to set the attack skill to Certain Hit, because this formula already deals with misses.
    
  
  

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