Monster Design – J. Baseline and the Cave Rays

The core system of Symbaroum proposes that monsters be evaluated on the basis of how many points of experience went into their construction. Personally I find that a lacking measure of actual difficulty.

A monster with Terrify and Resolute 7 is much less dangerous than a monster with Terrify and Resolute 15, but on paper they would be the same challenge level.

When I construct monsters, I tend to pick their abilities first and then put together a selection of attributes that set those abilities to a reasonable difficulty level. The level of modifiers you put on different tests has a much larger impact on difficulty than just the number of experience points that were invested in the character.

With this approach, you can design monsters that have great abilities but sub-optimal attribute selections for those abilities (Strangler and mediocre Cunning, for example) and easily spin off more dangerous variants of those creatures.

Joey Baseline

When I build enemies, I tend to adjust them against a baseline comparison level. If we assume that a character with 10 in an attribute has a 50% chance to succeed on a test of that attribute, then we can easily estimate how easy or hard every step of an interaction will be by seeing how it impacts Joey Baseline’s chance of success.

On a d20, every numerical face represents a 5% chance. Correspondingly, a shift in a single attribute point means a change of 5 percentage points up or down.

  • Against an enemy with an attribute of 10, J. Baseline has 50% chance of success.
  • Against an enemy with an attribute of 9, J. Baseline has 55% chance of success.
  • Against an enemy with an attribute of 15, J. Baseline has 25% chance of success.

Joey Baseline against a basic Cave Ray

Cave Rays were a monster I created for my home campaign, and part of the subterranean biome adversaries I detailed in the Monster Codex. They lurk underwater and wait for a target to come up to the water’s edge, then they jump out and wrap around their prey and attempt to drag them into the water to drown. They are evolved to hunt sightless amphibians in the dark, and are thus not optimal predators against wary adventurers with torches and keen eyes.

They have Westling (Novice) and Acrobatics (Adept), allowing them to grapple and throw targets, as well as avoid Free Attacks from disengaging in melee, and leaping up from prone position.

Joey Baseline has…

  • 45% chance to spot it lurking (Discreet 11)
  • 25% chance to hit it (Quick 15)
    • if you hit, it has zero armor and 10 Toughness / 5 Pain Threshold
  • 55% chance to avoid getting hit by it (Accurate 9)
    • 50% chance to avoid getting thrown or grappled (Strong 10)
    • If grappled, all other cave rays have Advantage (+10% hit chance)

Structured like this, we can assume a few things:

  • In a group of six players, roughly three of the group could become aware of the cave rays before they attack.
  • Even if they spot the rays, only one or two of the group will succeed in hitting them
  • If the players do hit them, the cave rays will die from just a few attacks
  • 3/6 players should be able to avoid the first wave of attacks
    • Half of the hit players should become grappled or thrown into the water
    • Grappled characters go from having a 55% chance to avoid being hit to having a 45% chance to avoid being hit
    • Thrown characters take 2 damage ignoring armor

This is what I consider a “trap monster” encounter. The monster lies in wait, inconveniences the players, and might then scatter or flee after having inflicted a few points of damage. The Cave Rays are unlikely to wipe a party, but have a high likelihood of surviving at least a couple of rounds trying to drag a player character to choke in an underground puddle.

And the difficulty of the encounter is easy to adjust. If we alter just a few of the Cave Rays’ attributes, we can dramatically alter the dynamics of the engagement:

Joey Baseline against a Cave Ray with modified attributes

Let’s modify the cave rays a bit. Instead of being a sighted predator that waits for a dumb target to volunteer to be drowned, let’s have the cave ray be dumb and blind but very strong. For this example, let’s just swap around the four attributes we actually use for this encounter: Discreet, Quick, Accurate, and Strong. Let’s swap Discreet and Accurate, and Quick and Strong.

  • 55% chance to spot it lurking (Discreet 9)
  • 50% chance to hit it (Quick 10)
    • if you hit, it has zero armor and 15 Toughness / 8 Pain Threshold
  • 45% chance to avoid getting hit by it (Accurate 11)
    • 25% chance to avoid getting thrown or grappled (Strong 15)
    • If grappled, all other cave rays have Advantage (+10% hit chance)

It’s now +10 percentage points easier to spot them. It’s +25 points easier to hit them. It’s -10 points harder to avoid being hit by them, and -25 points harder to avoid being grappled. If the group has a character with high Vigilant, they are unlikely to ever be surprised by these aquatic beasts, and once spotted they can easily be dispatched from a distance (although they now have much more hit points and a more difficult pain threshold to hit). However, if the group slips up and doesn’t spot a colony of rays, they are much more dangerous. If someone gets hit they are unlikely to escape a grapple, and once grappled they have only a 35% chance to avoid further hits.

This has effectively turned the cave rays from a trap encounter to a straight-up fight. The players are likely to see the cave rays coming ahead of a fight, so they can make preparations against these amphibians – but if the players get careless it’s quite likely that a few of their characters will get mobbed by the rays and dragged underwater.

We can also alter the encounter by just adjusting what abilities the monster has:

Joey Baseline against a Cave Ray with modified abilities

Let’s go back to the original line of attributes, but instead of Wrestling (Novice) and Acrobatics (Adept), we give the cave rays Wresting (Adept).

  • 45% chance to spot it lurking (Discreet 11)
  • 25% chance to hit it (Quick 15)
    • if you hit, it has zero armor and 10 Toughness / 5 Pain Threshold
    • if you miss it, 50% chance to avoid being thrown prone in retaliation (Strong 10)
  • 55% chance to avoid getting hit by it (Accurate 9)
    • 50% chance to avoid getting thrown or grappled (Strong 10)
    • If grappled, all other cave rays have Advantage (+10% hit chance)

This simple ability shift has just made it so that half of the Baselines who attack a cave ray in melee get thrown prone, taking 2 damage that ignores armor and leaving them stunned and prone. This is a reaction so it happens on the attacking players’ turn, leaving them totally open to attacks from Advantage after their failed attack.

75% of Joey Baselines will miss the cave ray in melee, and if half of them get thrown that means that attacking the ray carries a 37.5% risk to be left on the ground. In a party of six, that’d mean two characters being thrown to the ground in retaliation every round, and another one or two from ray attacks.

When I ran the Cave Rays for my own group they were fairly high level so I even gave the rays Acrobatics (Master) to allow them to use the player characters as shields. It turned into some serious slapstick when the party’s slayer tried to dislodge a ray that was wrapped around his brother, and when he brought the hammer down the ray twisted to make him hit his own brother in the face – knocking him out immediately.


Another important factor to account for when putting together a monster for an encounter is to ask yourself: What degree of resistance was this adversary expecting? Will they flee if that is exceeded? Are they committed to fight until they die?

The Cave Rays are cowardly opportunists used to capturing prey far less combative than player characters. If the players kill one or two of them the rays should start to scatter.


Without altering much about the Cave Rays stat block you can easily make several different adversaries with different tactics and manners, and different behaviors in a fight:

  • Tanglefoot Roots – An area surrounding a blessed grove might be protected by living roots and vines that will try to cast intruders off-balance. They will not pursue enemies but will attempt to bar entry into their grove.
  • Torchbearer Scrummers – A torchbearer sports team might have a lot of use for a cheap tactic that revolves around throwing opponents to the ground and stunning them. They will not attempt to knock out prone opponents but instead take advantage of the shift in action economy to score goals.
  • Brawling Bar Patrons – In a bar fight you could easily have unarmed combatants trying to grapple the players and throw them into a pile of kicks and punches.
  • Subject Collectors – Constructs that silently patrol an abandoned dungeon looking to capture subjects and bring them to a laboratory for long-forgotten experiments.

The players may not make the immediate connection that they are fighting something mechanically identical to the cave rays, because the look and feel of the encounter is different. But once the slapstick starts, maybe they’ll go “oh it’s another one of those nights I spend entirely on my back.”





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