Considering Monster Design

Years ago a friend summarized some hero design guidelines for me. Three of the key ones were

1. Have a way to get to the action.
2. Have a way to survive the action.
3. Have a way to take part in the action.

There is also an implicit ‘have a reason to be involved’, but that is perhaps more looking to campaign setting or background rather than the mechanical implementation. In this context it might be more important for character placement than for character design.

In any case, I think much the same guidelines apply to monster design.

Existing Game Application

In D&D 4e the above guidelines are applied pretty directly and literally. Armor Class, hit points, attack bonus, and so on are more or less directly derived from the monster level, then adjusted to taste. Some monsters may be weak-minded (lower Will defense), but really tough (higher Fortitude defense).

Trailblazer did a lot of analysis and developed something called “The Spine” that maps Challenge Rating to average Armor Class, hit points, damage, saves, and so on. Their analysis led to the conclusion that you actually have a fair bit of latitude in changes before the CR is particularly affected. For instance, increasing a monster from a d8 Hit Die to a d10 Hit Die is unlikely to substantively change the challenge in defeating them.

D&D 3.x… does not do this explicitly. It is evident that some Hit Dice (Dragon, Outsider) are worth more than others (Animal) but little more is done explicitly. This leads to some serious dissociation between Hit Dice and CR. Sometimes you have monsters with CR close to their HD (many outsiders), often you have monsters with CR much lower than their HD (lots of undead, animals, even dragons – though the last tend to be under-CRed, so it’s tougher to judge there). Because of differences in “Type Hit Die Value” you can get some wildly dissociated Hit Die and CR values.

When revising the monster types I found that when changing the number and type of Hit Dice to produce similar attack bonus and hit points I could often come fairly close. For example, when changing the Undead type to be a subtype of Construct I found that changing the d12 HD and +1/2 BAB progression to d10 (plus Construct bonus hit points) and +3/4 BAB progression I would often get about the same results. Similarly, increasing a Fey’s HD from d6 to d8 and BAB progression to +3/4, then giving it the same attack bonus, would often work out to about the same number of hit points as the original (though this case is helped somewhat by Fey generally not having very many Hit Dice – if there were Fey with 18 Hit Dice things might be a little different).

To a significant extent, 3.x monster special abilities are roughly appropriate to their Challenge Rating. There are exceptions (a CR 12 dragon with DR 10/magic might as well not have the damage resistance when it comes to facing the heroes because they will have magic weapons or use alternate means, though it is handy when facing mundane characters) but for the most part monsters have abilities that let them play in the sandbox with others monsters and characters of about the same level.

What this Means, My Conclusions and Assumptions

Monsters in the various monster books have abilities appropriate to their CR, and Hit Dice and attack bonuses and Armor Class and the like similarly appropriate to their CR. In redesigning monsters to fit the KJD-IMC rules (and later, Echelon), as long as I can get close to the existing values I should end up with something playable.

In Echelon different character types (warrior, wizard, and so on) should be roughly comparable in ability. This is something D&D 3.x doesn’t do so well (as described in my first Failures of D&D 3.5 post) but for the sake of simplicity I’m going to pretend the same is true in D&D 3.x.

With the base Hit Die size being d8 and Base Attack Bonus progression of +3/4 for most monsters, and these being roughly proportionate to the Challenge Rating, and racial Hit Dice being generally inferior to class levels, it should be reasonably safe to substitute class levels equal to the creature’s Challenge Rating, then give the creature the racial abilities appropriate to its level.

Examples

I expect to do some more examples in tomorrow’s post, but I will start with a couple here to demonstrate.

Frost Giant CR9

For the sake of argument, let’s do this as a CR9 creature, and thus with nine character levels. We’re going to have to strip it down somewhat because we’re removing and replacing all 14 Hit Dice. For instance, all feats are gone (but at least four will come available again from class levels), all Hit Dice (obviously), three ability score bumps (assume they were on Strength), all ranks in skills (but treat his chosen skills as racial skills). He gets to keep cold immunity, low-light vision, rock catching and throwing, and vulnerability to fire.

Note that in both cases I have left them with the same base ability scores (as if they had rolled 10s and 11s across the board), though I think it would be reasonable to have the cleric swap a few scores around, if only a couple of points each from Strength and Constitution to Wisdom and Charisma. I also have not given them any particular equipment beyond a chain shirt and a greataxe; at this level I would expect each of them to have some better gear (masterwork gear at least, probably some supporting magic items). I haven’t allocated all resources due to the cleric (only Power Attack, out of four feats he is entitled to, and only the domain bonus spells). In both cases I would expect to choose feats comparable to those available to PCs, so they should each have a little more than they have shown below.

First, we’ll take a look at a Frost Giant Barbarian.

Frost Giant Barbarian 9 (CR9)

Next, let’s look at a cleric. I am skipping some of the choices available because I don’t feel like assigning the full set of spells right now, nor looking for a better set of feats than the default. I think it sufficient to select domain spells and indicate how many spell slots are available, and mark how many feat slots are still available.

Frost Giant Cleric 9 (CR9)

I haven’t actually play-tested these, but they look fairly reasonable to me. A human barbarian or cleric at this level would be considered a CR 9 threat. These characters are a little more powerful (higher Strength and Constitution than likely in a human, plus cold immunity (and matching and obvious fire vulnerability, so it’s not that much of a benefit in a fight). Rock catching and throwing aren’t worth very much. This looks fairly comparable to the 14 HD frost giant from the RSRD.

All in all I think these look credible, and give me a much better base for drawing Challenge Rating and Hit Dice closer to equivalency – and for adding further class levels to monsters (or at least frost giants). I’ll have to explore with some other monsters tomorrow.