I woke up this morning with a cool idea for how to handle hydras in D&D. A quick check of the 5^th Edition Monster Manual, however, alerted me to the fact that 5^th Edition basically already did it that way.

Well played, 5^th Edition.

Upon further investigation, it became clear that my subconscious had dredged up a goulash of 3^rd Edition, 2^nd Edition, and OD&D mechanics and then regurgitated them.

Which, upon further consideration is a pretty good summary of the design methodology of 5^th Edition. (This is not a critique.)

Hydras, in D&D 5^th Edition, work like this:

Multiple Heads. The hydra has five heads. While it has more than one head, the hydra has advantage on saving throws against being blinded, charmed, deafened, frightened, stunned, and knocked unconscious.

Whenever the hydra takes 25 or more damage in a single turn, one of its heads dies. If all of its heads die, the hydra dies.

At the end of its turn, it grows two heads for each of its heads that died since its last turn, unless it has taken fire damage since its last turn. The hydra regains 10 hit points for each head regrown in this way.

The heads give a couple other advantages (extra opportunity attacks, it can sleep while still having one head awake to keep watch), but that’s the fundamental mechanic that models the classic hydra.

There are a couple of changes to this approach that I’d like to experiment with:

1. Eliminate the concept of “total hit points” entirely. You can’t kill a hydra unless you chop off all of its heads.
2. Tweak the mechanic so that you can eliminate more than one head per turn.

So if a fighter gets in there and deals 50 points of damage, his flurrying blades will have hacked off a couple of heads at once. Then maybe the rogue leaps onto its back, deals another 25 points of damage, and hacks off a third head. On the hydra’s turn, it will grow back six heads (two for each severed head).

REVISING THE HYDRA

Thus we can say that a hydra should be mechanically defined as:

• # of heads
• A damage threshold at which it loses a head
• At the end of its next turn or after X rounds it can regrow two heads if it has a severed head
• A sealing condition (usually a type of damage) that prevents
• Dies when it runs out heads.

The “Hit Points” entry of their stat block would be listed as “Special”: They only die if they run out of heads.

Here’s what our revised hydra special abilities would look like:

Hydroid. The hydra has five heads. For every 25 points of damage the hydra suffers, one of its heads dies. If all of its heads die, the hydra dies.

At the end of its turn, the hydra grows two heads for each of its severed heads, unless it has taken fire damage since the head was severed.

Multiple Heads. While the hydra has more than one head, it has advantage on saving throws against being blinded, charmed, deafened, frightened, stunned, and knocked unconscious.

For each additional head beyond one, it gets an extra reaction that can be used only for opportunity attacks.

While the hydra sleeps, at least one of its heads is awake.

CREATING HYDROID CREATURES

These mechanics can be used as the basis for other hydroid creatures. Here are some proposed guidelines for doing so.

Damage Threshold. This is the number of hit points required to chop off one of the hydroid appendages. These numbers are loosely based around the idea that a character of the appropriate level should be roughly capable of taking out one head per turn.

I’d recommend halving this value if the sealing damage type or other condition is an unusual one. (This would mean that the killing the monster would typically require killing the heads faster than they can grow back.)

# of Heads. Using the Creating Quick Monster Stats table on p. 274 of the Dungeon Master’s Guide, multiply the minimum hit points for your selected CR by 0.75 and then divide by the damage threshold listed above for its CR.

For example, a CR 10 creature would have 206 hp using the table above, so multiply by 0.75 (154) and then divide by 25 (per the damage threshold table above) to determine that your monster should have six heads.

(This is based strictly on reverse-engineering the existing hydra stat block and it’s unclear if it holds up in practice. It seems to pretty reliably give you 4-8 heads, so you could also probably just get away with slotting in 5-6 heads and not worrying about it.)

You can also use this method to very quickly adapt existing stat blocks. For example, if you wanted to have a hydroid warg (CR ½) you’d take the warg’s current hit point total of 26, multiple by 0.75 (19.5), and then divide by 10. The hydroid warg would start with two heads.

Variant: Maximum Number of Heads. In 2^nd Edition, Lernaen hydras could grow maximum of 12 heads. In 3^rd Edition, they were limited to no more than twice its original number of heads. You might consider doing the same for some hydroid creatures.

DESIGN NOTES

Hydras have a well-known gimmick: They regrow their heads unless you cauterize the stumps with fire. It’s a fun gimmick the can create an encounter which mechanically feels different from other encounters. The only problem is that, because the hydra still has a hit points that’s easier to wipe out than its heads, the mechanical gimmick is irrelevant: There’s often little or no advantage to pursuing it, so parties will just bypass it.

This is boring.

So we fix it by eliminating the bypass. Just like you can’t bypass a troll’s regeneration by just dealing lots of hit point damage to it, you can’t bypass a hydra’s heads.

And, just as regeneration mechanics were created for trolls and now underlie a whole bunch of creatures, these hydroid mechanics can also be used for all kinds of things. We’ll take a look at several examples of this tomorrow.

Go to Part 2

This will start off with a bit of a quick review of the advantage/disadvantage system, so feel free to skip down a bit if you’re already thoroughly familiar with that.

In 5th Edition, various circumstances and abilities grant either advantage or disadvantage to a character attempting an action: If you have advantage, you roll 2d20 and keep the higher result. If you have disadvantage, you roll 2d20 and keep the lower result. If you have both advantage and disadvantage, they cancel out (and you just roll 1d20). And they do not stack (so no matter how many things are giving you advantage, for example, you still only roll 2d20 and keep the highest, not 3d20 or 5d20 or 10d20), which also means that even one factor granting advantage will cancel out any amount of disadvantage (and vice versa).

There are several benefits of the advantage/disadvantage system compared to giving circumstantial modifiers to the die rolls:

• The modifiers you’re rolling against are not in constant flux, reducing the amount of in-game calculation required.
• It is viscerally pleasing and immediately rewarding to roll 2d20 and take the higher/lower result. It’s fun to do and you can literally see how your advantage benefited you or your disadvantage cost you by looking at the result on your gained/discarded die.
• It helps maintain the “bounded accuracy” of the system; advantage helps you, but you can still only get die results of 1 to 20.
• “Advantage” and “disadvantage” are incredibly useful terms of art, which designers, scenario writers, and DMs can quickly and efficiently use for any number of purposes. For DMs, in particular, they provide a very simple way to make a fast ruling.

The reasons for not allowing advantage or disadvantage to stack are:

• To maintain the simplicity of that fast, efficient DM’s ruling. Once you’ve determined that something in the situation grants advantage, for example, you don’t have to keep thinking about all the other things that might grant advantage: You have advantage. Move forward. Roll the dice.
• You don’t need complicated stacking rules, nor do you need to allow abilities to stack in potentially absurd ways. This removes one vector by which an RPG system filled with myriad options can suddenly break from the unexpected combination of those options.
• There are some mathematical effects of allowing advantage to stack multiple d20’s into a single roll, the most notable of which, in my opinion, is that your percentage chance of scoring a critical hit radically expands. (This last point is debatable, however, as many would argue that this is perfectly reasonable if you’re enjoying a massively advantageous situation. It also only applies to actually stacking additional dice, but not to the scenario in which you stack all advantage and all disadvantage and then compare the totals to see whether advantage, disadvantage, or neither applies.)

This system has one additional advantage (pun intended) that I want to call specific attention to: The simple, clear-cut mechanical concept of “advantage” also encourages players to engage creatively with the game world in order to create fictional positioning that grants them advantage.

Another example of this that I’ve seen in actual play is Numenera‘s concept of an “asset” — on any given task, PCs can have up to two assets, each of which shifts the difficulty of the task by one step. The first asset “slot,” so to speak, is often occupied by having the right tool for the job. The second asset slot is usually dependent on having some sort of advantageous situation in the game world, and this naturally results in players seeking to create those in-world circumstances that will give them an asset on a task.

In both cases, the clear-cut term of art coupled to the specific fictional situation in the game world reinforces the fiction-mechanics cycle. The mechanic thus, almost paradoxically, encourages players to engage in the game in non-mechanical ways: It’s not enough to just “play your character sheet” by saying “I hit the orc with my +6 attack bonus,” because the mechanics are no longer confined to the bonuses on your character sheet.

Arguably, of course, you can get the same benefit from any system that allows GMs to assign situational bonuses and penalties. But in actual practice, the clear-cut mechanical concept with a term of art attached to it provides a common framework. People just talk about and think about “advantage” and “assets” in ways that they don’t talk about and think about a miscellanea of +1, +2, or +5 bonuses.

THE PROBLEM

Speaking of actual practice, however, this final — and arguably most important — aspect of advantage tends to frequently disappear at the table.

The problem, ironically, is the very versatility of the system. Because advantage is such an easy mechanical hook to use, the designers of the game have used it to model all sorts of things. It’s hard-coded into everything from class abilities to spells to magic items. For example:

Dwarven Resilience. You have advantage on saving throws against poison, and you have resistance against poison damage (explained in Chapter 9).

Or:

Beacon of Hope. This spell bestows hope and vitality. Choose any number of creatures within range. For the duration, each target has advantage on Wisdom saving throws and death saving throws, and regains the maximum number of hit points possible from any healing.

Or:

Boots of Elvenkind. While you wear these boots, your steps make no sound, regardless of the surface you are moving across. You also have advantage on Dexterity (Stealth) checks that rely on moving silently.

Because advantage doesn’t stack, however, tension is created between the designer’s utility and the DM’s utility: If a character has hard-coded advantage from equipment or racial abilities or whatever, the DM immediately loses the ability to meaningfully model the game world through advantage and the player is simultaneously discouraged from engaging with the game world in order to create favorable circumstances.

This is not a desirable outcome: Basically every time the game hard-codes advantage in this way, it makes the game less interesting in actual play.

Numenera recognizes the same basic problem, which is why it provides two asset “slots.” The solution is not quite so straightforward for 5th Edition because there are so many pieces of equipment, for example, that provide identical forms of advantage, that simply providing two slots will simply create min-max builds that stack multiple advantage and still shut down situational creativity (because both slots will already be filled).

But we can find a solution, I think, through parallel thinking. And by simply cutting straight to the heart of the matter.

SITUATIONAL ADVANTAGE

Situational advantage is any advantage which is derived from a character’s immediate circumstances; particularly and specifically those cases of advantage resulting from characters taking actions or positioning themselves in order to create specific situations which grant them advantage.

Situational advantage, and only situational advantage, stacks with other advantage:

• If you have hard-coded advantage (e.g., the advantage against poison damage from dwarven resilience) and situational advantage (e.g., the character manages to dilute the poison before being forced to swallow it), then you roll 3d20 and take the best result.
• One source of disadvantage can cancel EITHER all hard-coded advantage or all situational advantage, but not both. (So if you have all three, you’d still have advantage and roll 2d20 while keeping the best result.)
• If you have two or more sources of disadvantage, then they will cancel both hard-coded and situational advantage. (You would simply roll 1d20 and resolve the action check normally.)

Note that not all forms of advantage appearing in the rulebook are necessarily hard-coded. Some describe situational advantage. (The optional rules for flanking, for example.)

What about advantage from spells? Is the advantage provided by a spell situational? There is a potentially simulationist argument that they are (or perhaps that some subset of them are, although that way probably lies madness). But the primary meta-game point of all this is to encourage players to think creatively as they engage with the game world instead of just throwing a prepackaged block of mechanics at a problem.

And a spell, after all, boils down to a prepackaged block of mechanics.

So if I had to make an ironclad rule, I would say that advantage from spells is always considered hard-coded advantage.

Fortunately, the entire point of situational advantage is to prevent hard-coded rules from disempowering the GM. So I will by happy to override this ironclad rule whenever players think creatively in order to create situational advantages from their spells. For example, by using a create food and water spell to water down the poison before it’s fed to the dwarf.

Interrogation checks are made to resolve the controlled questioning of prisoners or suspects: People who have (or who you believe might have) a reason to withhold information from you.  Obtaining information through other forms of social interaction (questioning witnesses or chatting someone up at a social soiree, for example) is certainly possible, but may not be the right fit for these mechanics.

When interrogating a subject, the questioner can choose one of two approaches:

DIPLOMACY: These are “soft” methods of interrogation. Manipulation, seduction, a building of trust, a promise of quid pro quo.

INTIMIDATE: These are “hard” methods of interrogation. This doesn’t cover actual torture, but it does include aggressive techniques, threats of violence, and the like.

The appropriate interrogation skill is used to make a check against DC 10 + the subject’s HD + the subject’s Wisdom modifier. On a success, the interrogator gains one piece of information. Additional interrogation checks can be attempted, but each additional check applies a cumulative +2 modifier to the DC of the check.

After two failures, the interrogation will provide no more useful information. (The subject has broken down or their lawyer has shown up or they simple have no more useful information to share.)

ESCALATION

Each interrogation technique can be escalated to the next level:

BRIBERY: Diplomacy-based interrogations can be enhanced with bribery. If a sufficiently large bribe is offered, the interrogator gains a +10 circumstance bonus to their interrogation checks for the rest of the interrogation. (Alternatively, you could use these advanced guidelines for determining the efficacy of a specific bribe.)

TORTURE: Intimidation-based interrogations can be escalated to actual torture. This involves inflicting actual physical damage and pain. (Or possibly inflicting the same on comrades or loved ones.) The target must make a Will save at DC 10 + the damage dealt by the torturer. If the subject fails the Will save, the interrogator gains a +10 circumstance bonus on their next interrogation check. (Of course, they can continue torturing the subject in order to gain the same bonus again.)

Both of these techniques, however, represent a gamble: Under the temptation of bribery or the desperation of torture subjects may invent information or say whatever they think the interrogator wants to hear. There’s a flat 25% chance of false information when giving a bribe. There’s a cumulative 10% chance of false information when using torture. (So after torturing a subject for the third time, there will be a 30% chance of false information.)

SUPPORTING SKILLS

A couple of other skills can be useful in interrogations.

BLUFF: Subjects can attempt to provide false information with a Bluff check. If the check fails, however, the interrogator has seen through their lie and can immediately attempt another interrogation check with a +2 circumstance bonus to get the truth out of them. (All of the modifiers from their previous test still apply.)

SENSE MOTIVE: Sense Motive can, obviously, be used to oppose a subject’s Bluff checks. It might also be useful for determining what threats or promises would make for the most effective intimidation or bribery (offering a circumstance bonus in accordance with the guidelines for aiding another, but perhaps inflicting penalties if the check goes awry).

OTHER SKILLS: Other skills can also be used situationally to aid the interrogation check. For example, demonstrating a bit of legerdemain with Sleight of Hand might impress a social contact. Or a Knowledge check might produce information that would endear an expert. Use the guidelines for aiding another to resolve these checks.

GOOD COP / BAD COP

An interrogation team can play good cop / bad cop by switching their interrogation technique (from Diplomacy to Intimidation or vice versa). If their first interrogation check after the swap is successful, they can negate a previous failure. (This will allow them to prolong the interrogation.)

It’s exceptionally difficult to play good cop to your own bad cop: Apply a -10 circumstance penalty to the first check of an individual interrogator after the switch in approach.

DESIGN NOTES

Kenneth Hite has a technique he uses in investigation games: When the characters have gained all the information they’re going to get from a scene, he holds up a sign that says “SCENE OVER” or “DONE”. The statement cues the players to let them know that there’s no reward to be gained by continuing to ransack the apartment, while using a sign is less intrusive on the natural flow of the scene (so if there’s something they still want to accomplish in this scene of a non-investigative nature, the scene can continue without the GM unduly harshing the vibe).

The core of this interrogation mechanic is designed to do something similar: It’s sending a clear and specific “we’re done here” message to the players, allowing you to perform a clean cut that keeps the pacing tight.

It also has the added benefit of answering for the GM, “How much information does this guy really know?” in situations where that isn’t immediately clear. (This is a question I frequently struggle with when some random mook gets interrogated.)

Collectively, that’s why the difficulty cranks up after each question: I want the mechanic to terminate the interrogation for me.

You might also want to check out my Advanced Rules for Diplomacy. And my thoughts on Social Skills and PCs might also be of interest.

Numenera features player-facing mechanics: Whenever an action requires diced resolution, it’s always the player who rolls the dice. If a PC is being attacked, the player rolls to dodge. If the PC is attacking, the player rolls to hit. There are a lot of advantages to this system, particularly in the ways that it seamlessly interacts with the pool-spend, GM intrusion, and difficulty adjustment mechanics.

But the drawback of player-faced mechanics is that they can’t be used to resolve contests between NPCs. Numenera opts for one of two relatively straightforward work-arounds (to be used at the GM’s discretion):

(1) In keeping with other mechanics in the system, the NPC with the highest level automatically succeeds.

(2) If that’s undesirable for some reason, “the GM should designate a player to roll for one of the NPCs. Often, the choice is obvious. For example, a character who has a trained attack animal should roll when her pet attacks enemies.”

The problem with this method is that, because of the way NPC stat blocks and pools work in Numenera, the result doesn’t factor in the NPC’s skill whatsoever: There is no modifier applied to the roll, so an NPC that’s level 2 at attacking has the exact same chance of hitting an NPC opponent as an NPC that has a level 7 attack.

What makes the problem even more vexing is that a large number of character options feature allied NPCs (like the aforementioned trained attack animal).

NPC ALLIES

NPC allies have an effort pool equal to level x 3 per day.

NPC allies also gain one recovery roll per day. This recovery roll can be used as an action at any time, restoring 1d6 + level points to their effort pool.

When rolling for an NPC, adjust the die roll by +1 or -1 per difference in level. For example, a level 5 NPC attempting a level 3 task would gain a +2 bonus to their die roll. The same NPC attempting a level 7 task would suffer a -2 penalty to their die roll.

DESIGN NOTES

These rules are short, simple, and to the point. They present a minor disruption to the purely player-faced mechanics, but without bulking out an NPC to have the same complexity as a PC. (In terms of utility, it’s particularly important that the mechanics don’t actually require a specialized NPC stat block: The effort pool can be easily derived from any existing NPC or creature.)

In actual play, the addition of the effort pool provides just enough interest to make running an NPC ally interesting while the level adjustment to the die roll for NPC vs. NPC actions provides enough distinction between characters that their interactions don’t feel flat or artificial.

These rules can be found in the “House Rules” section of my Numenera system cheat sheet.

The effect of prolonged exposure to extreme temperatures in Trail of Cthulhu is very straight-forward: Investigators are considered to be hurt, resulting in them suffering a +1 difficulty on all tests.

The designers of Eternal Lies had a desire to make exposure to extreme heat more mechanically interesting and they introduced a rudimentary heat track. I found their treatment interesting, but wanted something a little more robust (particularly when it came to treatment and recovery). These mechanics are specifically designed for desert travel.

(They’re also not exactly “untested”, but I don’t have a series of posts called “minimally tested”, so here we go.)

HEAT EXHAUSTION TRACK

0. Not suffering heat.

1. Can only make spends after first resting for 10 minutes (to gather their thoughts and spirits).

2. Difficulty of contests +1 (including hit thresholds).

3. Difficulty of tests at +1.

4. Can only make 1 spend per day and must make it in the morning after a good night’s sleep, before the day’s temperatures begin to rise.

5. Cannot make any spends.

6. Can only refresh 1 Health per day. If Heat Track would advance, it remains at 6 but character suffers 1 damage.

ADVANCING HEAT

Desert Travel: +1 Heat track per day. Characters who traveled during the day are considered to be under extreme heat conditions for the purposes of treating heat.

Camping: Characters who take a rest from traveling by camping for one full day are considered to be in favorable conditions for the purposes of treating heat.

Oasis: An oasis or similar place of significant respite may be considered “controlled conditions” for the purposes of treating heat.

TREATING HEAT

A given character can be treated for heat once per day.

First Aid/Medicine in favorable conditions to prevent advancement or reduce position on the heat track by 1.

First Aid/Medicine (difficulty 3 + heat track) in extreme heat conditions to prevent advancement or reduce position on the heat track.

First Aid 1 / Medicine 1 in controlled conditions to bring an investigator back to 0.