Monday, February 23, 2009

AC and HP Scaling

All versions of D&D to date have used two main defenses in combat: Armor Class (or some standin such as Reflex or Will) and Hit Points. Typically an attacker first determines if he hits (rolls vs. AC) and then determines how hard he hits (rolls damage). In most versions of D&D, AC and HP both increase with monster level. This forces PCs to constantly keep up or risk being useless in combat. It also creates some problems -- the designer needs to find a way to scale PC damage up with level. That 1d8 long sword just doesn't pack the same punch against a 60 HP Fire Giant as it did against a 6 HP Orc. Various methods that attempted to resolve this problem include magic weapons, AD&D's multiple attacks for fighter types, spells that do more damage with level, and increasing amounts of Sneak Attack damage (multiplier in AD&D, SA in 3E/4E).

Increasing monster HP has a few ramifications:
- It makes monsters less vulnerable to the "golden BB" -- As we all know, D20s are highly variable. A first level character might roll a 20 and hit a powerful monster. By giving Smaug many HP, then that hit will not take out the powerful dragon. This basically reduces the variability of the game in one direction.
- If AC is the same as other monsters, it increases the "screen time" and staying power of a monster, like a Solo or Elite monster.
- If AC is lower than other monsters, it creates a different feeling monster (4E's Brute -- easy to hit but absorbs a lot of punishment)
- If AC is higher than other monsters, it basically creates a higher level monster.

Note that the only one of these that relates to the player's level is the Golden BB issue. If we can find a way to solve the Golden BB issue, then we can keep monster HP "fixed" regardless of level and just vary it in regards to AC. Then AC becomes our only factor that changes with level. We then deftly side step the whole escalating damage issue altogether. This vastly simplifies our entire combat system. Also, it allows monsters to be used over a wider variety of "levels" -- as anyone that's fought a higher-level monster in 4E knows, lower level characters just can't tear through the massive HP fast enough. And in 1E, a higher level monster may be able to one-shot a PC just because it does so much damage.

To resolve the Golden BB issue, you can do a few things:
- Set defenses/ACs high enough that lower-than-desired characters just can't hit them.
- Set up some sort of Deus Ex Machina mechanic to ensure that the campaign's arch-villain doesn't get one shotted by a first level hero in the first scene.
- Not worry about it -- a single archer brought down Smaug, and sometimes the heros get lucky.

Honestly, I prefer the middle option (deus ex machina). This is because of the "What is Good for the Goose" rule, in part -- I don't want PCs to be one shotted by giant rats at level 10. Also, I don't want to rely soley on manipulating ACs, because then % chance to hits might get so low or high that the game isn't fun anymore.

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