Design & Development
Monster Makeover
The Rust Monster



We're hoping this column becomes your window into roleplaying design and development—or at least the way we approach these things here at Wizards of the Coast. We'll handle a wide range of topics in weeks to come, from frank discussions about over- or underpowered material, to the design goals of a certain supplement, to what we think are the next big ideas for the Dungeons & Dragons game. All of this comes bundled with a healthy look at the people and events that are roleplaying R&D.

The creature sports two long antenna on its head, one beneath each eye...


In many ways, the art of development is the art of translation. The process of producing material for Dungeons & Dragons is a conversation between the gamers and R&D. Gamers tell us what they want (directly or indirectly) and R&D responds with new rules, story elements, and other stuff that we hope answers these requests.

In this conversation, a developer listens to both sides and, when necessary, shifts the material created by design to better match what gamers want (or perhaps need to hear). In other words, a designer creates what sounds cool and interesting, and a developer translates that into something practical, easy to use, and balanced.

One of the hallmarks of development lies in its continuing evolution. D&D is a relatively simple system to learn. If you can add a few numbers to a d20 roll, you can perform 90% of the math needed to play. The game’s complexity lies in the interaction between all of the exceptions and supplemental rules. A feat like Cleave, for example, is its own little rule. If you do not use Cleave, you do not need to know how it works.

In contrast, a developer needs to understand how all of the rules work together, and how new rules elements fit into the overall game. In addition, a developer needs to have a good grasp of the game’s story elements. A feat that allows a wizard to wear full plate might be balanced in a purely mechanical analysis of Armor Class, but it changes the world of D&D in a way that runs counter to what people want and expect. Merlin and Gandalf don’t run around in plate armor, so neither should wizards and sorcerers (without substantial penalty).

As development understands more and more about how D&D is working, we change our goals. D&D is a living rule set that, over time, changes to produce a more interesting, fun, and playable game. Each year, we learn more about what works, what doesn't work, and what new directions are worth exploring.

To help give you a better understanding of development and show how our approach evolves over time, I'm going to take a classic beastie from the Monster Manual and send it through the development gauntlet. At the end of the process, we'll have a creature that probably looks a lot different than the creature we started with. As I work through the monster, I'll provide commentary on the changes I've made, why I made them, and the goal of each one.

Tangent Alert!: To find out more about the rust monster, check out this month's Dragon Magazine, #346. Inside, you'll find The Ecology of the Rust Monster, and several anecdotes of its appearance -- including Gary Gygax's Tales of Rust and Gloom.

Keep in mind throughout this process that development is usually a team process. It's important to have a diverse array of opinions on what works in a monster, what it aims to do, and how to develop it. Development is as much art as it is science, and it helps to have more than one opinion when dealing with issues involving personal taste, feel, and preferences—particularly when we’re reading the tea leaves to figure out what you guys want!

Monster Makeover: The Rust Monster

The first critter I'm going to tackle is the "lovable" rust monster. According to gaming legend, the rust monster entered D&D annals when Gary Gygax found a cool looking plastic toy in the same scale as the miniatures his gaming group used. Obviously, the plastic critter needed stats. Thus, the rust monster was born.

The 1st edition DMG featured an amusing, one panel cartoon of a terrified, fully armored fighter leaping into a wizard's protective arms. The source of our doughty fighter's terror? An approaching rust monster. To this day, the rust monster is a great creature because as soon as one skitters around the corner, it elicits an immediate, extreme reaction from the party. No one wants their beloved magic sword and expensive armor turned into a pile of red dust! A fight against a rust monster is invariably interesting (in the Chinese proverb sense of the word) and memorable.

Unfortunately, the rust monster's mechanics could use some work. Within the context of a single encounter, they're a lot of fun. But once your weapons and armor are rendered useless, the next encounter becomes that much more difficult. If you’ve invested thousands of gp into metal items, you better hope your DM is ready to hand over a ton of extra treasure to make up for your losses. At the very least, he needs to understand that the party's power level (especially for the fighter-types) is now behind the curve.

Homebrew Design V. WotC Design

Development's understanding of the game tells us that a monster who destroys your gear isn't fun. Simply put, it makes the next encounter prohibitively more difficult. The rust monster requires a lot more DM skill and a deeper understanding of the game than other creatures in its CR range.

However, that doesn't mean it cannot have a place in your game. A DM who understands how a rust monster works, or who builds his story to account for it, can have a lot of fun with the critter as written. If the PCs lose their weapons and armor, they might go into debt to a shady merchant to get replacements. That merchant can then play an important, interesting role in the campaign.

Development's responsibility is to create monsters that work in a way that’s easy to handle. The rust monster is CR 3, but it has a much bigger impact on the game than, say, a CR 3 ogre. We can't realistically put both those creatures on a random CR 3 monster table. Even worse, we don't want to send the message that monsters capable of destroying a party's gear are common opponents.

Instead, it's likely best for the game to let individual DMs create and use such effects as they need them in their campaigns. We don't want to encourage such effects, but there's no reason why a DM who knows what he's doing can't use them. In many ways, development assumes that an individual DM is like a computer who heartlessly applies the rules. This approach allows neophytes to trust the rules and experienced DMs to bend, fold, and mutilate them from the foundation of a workable, stable system.

Let's pretend that the rust monster is a brand new monster, turned over to the development team from design. It might help to open your Monster Manual to page 216 and follow along.

The first thing to check is the monster's basic stats. As a CR 3 critter, its hit points and AC are about what I expect—both are in the ballpark of an ogre, a good, touchstone CR 3 creature. Unfortunately, the rust monster's attack and damage don't come close to the ogre's offensive abilities. That attack includes the rust special ability.

And that's where things start to go wrong. Here's the offending rules material, lifted straight from the SRD:

Rust (Ex): A rust monster that makes a successful touch attack with its antennae causes the target metal to corrode, falling to pieces and becoming useless immediately. The touch can destroy up to a 10-foot cube of metal instantly. Magic armor and weapons, and other magic items made of metal, must succeed on a DC 17 Reflex save or be dissolved. The save DC is Constitution-based and includes a +4 racial bonus.

A metal weapon that deals damage to a rust monster corrodes immediately. Wooden, stone, and other nonmetallic weapons are unaffected.

Ugh! A rust monster is a great way to strip away the party's metal gear. At CR 3, chances are it often faces fighter-types in heavy armor who have relatively poor Reflex saves. A fighter without armor is a sitting duck, and a party that faces one of these things ends up either seriously outclassed for the rest of the adventure or forced to return to town to buy more armor. Neither of those situations screams epic, fantasy adventure. The rust monster carries a big sign that says, "Stop adventuring or die!"

One of development's goals is to facilitate play. We want people to get in multiple encounters each session, whether these are combat, roleplay, puzzles, or whatever. The rust monster brings any prospect of a balanced combat encounter to an end. The party might get lucky and kill it before it can destroy the fighter or paladin's armor, or the DM might be kind enough to include more armor in a treasure cache. If a monster needs such special consideration, we're better off toning down the ability. We could increase the CR, but the basic problem remains: This ability brings the adventure to a halt regardless of the party's level.

On the other hand, the concept of a monster that threatens metal items is pretty neat. It makes for an interesting fight, as the fighter might end up watching as the mage whacks on the creature with her staff. The rust monster is also a great helper beast for other creatures. Orcs might drive rust monsters forward against their enemies, ruining their foes' weapons and armor before moving to attack. The captain of the guards might use a captive rust monster to convince recalcitrant adventurers to hand over their weapons before they enter the city.

The problem with the rust ability is that it is far too punishing. With one hit, an armored character's AC drops by around 6 to 8 points for the rest of the adventure. If the party is short on cash, the PCs are stuck with sub-optimal armor. Taking a bigger picture view of things, how does this creature interact with warforged?

Design Notes: How do rust monsters affect warforged? Check out the Eberron Campaign Setting, p. 23:

"The iron in the body of a warforged makes him vulnerable to rusting grasp. The creature takes 2d6 points of damage from the spell (Reflex half; save DC 14 + caster's ability modifier). A warforged takes the same damage from a rust monster's touch (Reflex DC 17 half)." That's the same save DC listed in the Monster Manual entry; Con-based and with a +4 racial bonus.

We thought of everything. Or almost everything...
-- James Wyatt

The solution is to look at the design intent behind the rust monster, take the basic theme behind its abilities, and build new mechanics that realize the designer's goal without making the rust monster too powerful.

Here's a list of what I think the rust monster tries to achieve:

  • Scare the heavily armored guys.
  • Give leather-armored guys a chance to shine.
  • Make a memorable encounter where the PCs use different weapons than normal (wooden ones in this case).
  • Attack something other than the PCs' hit points. In this case, their AC and attacks via their weapons, armor, and shields.

The current rules do these things, but they also cause the complications I’ve discussed. So at this point we're looking at a redesign of the rust ability. We can alter the DC, or the amount of metal rusted at one time, but the fact remains that the root of our troubles is that the rust monster hits an item once (or is hit by it) and destroys it. The rust monster might still have the ability to turn metal into rust, but the current “one attack destruction” is too much; so, here's the redeveloped version:

Rust (Su): A rust monster that makes a successful touch attack with its antennae causes the target metal to corrode, warp, and crack. Any metal weapons, armor, and shields carried by a creature struck are weakened by this effect. The bonus to AC provided by an armor or shield drops by 2, to a minimum of 0. Weapons suffer a –2 penalty on attacks and damage, with a maximum penalty of –6. Magic armor and weapons, and other magic items made of metal, must succeed on a DC 17 Reflex save to resist this effect. The save DC is Constitution-based and includes a +4 racial bonus.

These penalties last for 10 minutes. A rust monster that spends 5 minutes devouring a metal object (whether magical or mundane) transforms it into rust, destroying it permanently.

A metal weapon that deals damage to a rust monster also suffers this warping and corroding effect. Wooden, stone, and other nonmetallic weapons are unaffected.

As you can see, the effect is now much less punishing. It slowly reduces an item's capabilities without crippling them. The recovery time also allow the PCs to rest for a bit, and then continue with the adventure. The rust monster still works well when paired with other creatures, especially if the next encounter takes place soon after the rust monster fight.

Finally, the rest of the creature bears some examination. It could use a slightly better secondary attack, especially after the PCs "solve" the rust monster and put away their metal gear. At that point, the beast is a push over. It also has more hit points and a better AC than an ogre, but those numbers are fine since the longer the rust monster sticks around in a fight, the more chances it has to show off its abilities.

To boost its attack, I swap out its Alertness feat for Multiattack. I also increase its Strength to 14, to improve its damage and attack. Its bite should inflict the standard 1d6 damage for a Medium creature, rather than 1d3.

The final change I make verges on personal preference. (Normally, the rest of the development team would be here to approve this decision.) I decide to re-allocate the rust monster's skill ranks into Hide and Move Silently, drop Track and replace it with Weapon Finesse, and give it a climb speed. The rust monster makes a good ambusher or lurking threat. If it can leap upon the party and get off the first attack from ambush, it slaps its rust ability on the party's fighter and gains a big edge in the fight.

And that's that. Normally, development would also read over the creature's flavor. The Monster Manual uses a different format than the standard monster presentation, so there's a lot less background to deal with. I'll skip that phase for this example.

Playtesting

To finish the process, I ran an encounter with an ogre mage, a rust monster, and an ogre against a party of three 6th-level adventurers ably played by D&D designer James Wyatt (as cleric), web guru Bart Carroll (flesh golem), and archmage of accounting Steven Montano (scout). The rust monster did great in the playtest. It stripped James's AC down by 6 points, allowing the ogre mage to fly in, flank, and drop him to single digit hit points with one mighty attack. Good times for the DM!

The playtest showed me that the climb speed and the bite attack were good changes. The rust monster managed to gnaw on James's cleric a few times, plus its climb speed allowed it to zoom past Steven's leather-armored scout and attack James. The one change I made is to boost the climb speed to increase the rust monster's maneuverability.

RUST MONSTER CR 3
Medium Aberration
Init +3; Senses darkvision 60 ft., scent; Listen +1, Spot +1

AC 18, touch 13, flat-footed 15
hp 27 (5 HD)
Fort +2, Ref +4, Will +5

Speed 40 ft. (8 squares), climb 40 ft.
Melee antennae touch +7 (rust) and
bite +5 (1d6+2)
Space 5 ft.; Reach 5 ft.
Base Atk +3; Grp +3

Abilities Str 14, Dex 17, Con 13, Int 2, Wis 13, Cha 8
Feats Multiattack, Weapon Finesse
Skills Climb +10, Hide +7, Move Silently +7

Rust (Su): A rust monster that makes a successful touch attack with its antennae causes the target metal to corrode, warp, and crack. Any metal weapons, armor, and shields carried by a creature struck are weakened by this effect. The bonus to AC provided by an armor or shield drops by 2, to a minimum of 0. Weapons suffer a –2 penalty on attacks and damage, with a maximum penalty of –6. Magic armor and weapons, and other magic items made of metal, must succeed on a DC 17 Reflex save or be dissolved. The save DC is Constitution-based and includes a +4 racial bonus.

These penalties last for 10 minutes. A rust monster that spends 5 minutes devouring a metal object (whether magical or mundane) transforms it into rust, destroying it permanently.

A metal weapon that deals damage to a rust monster also suffers this warping and corroding effect. Wooden, stone, and other nonmetallic weapons are unaffected.

Feedback

In addition to the article feedback we always hope to hear from you, we also wanted to ask if there's a monster currently in the game that you'd like to see redeveloped. Of course, we also love a good tale as well -- have one about rust monsters in your game and memorable encounters against them? Drop us a line at dndcolumn@wizards.com!


About the Author

Mike Mearls is the dark hope of chaotic evil: young, handsome, well endowed in abilities and aptitudes, thoroughly wicked, depraved, and capricious. Whomever harms Mearls had better not brag of it in the presence of one who will inform the Demoness Lolth!

Evil to the core, Mearls is cunning, and if the situation appears in doubt, he will use bribery and honeyed words to sway the balance in his favor. He is not at all adverse to gaining new recruits of any sort, and will gladly accept adventurers into the ranks, but he will test and try them continually. Those who arouse suspicion will be quietly murdered in their sleep; those with too much promise will be likewise dealt with, for Mearls wants no potential usurpers or threats to his domination.


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