“I leap from the ledge and try to land on the dragon’s back!” declares the barbarian. What follows? The answer is probably different at every table. Although improvisation is a staple in 5e to be celebrated, in these high-risk cases it’s often a boon for both the players and GM to know what kind of rolls might follow, what the monster might do in retaliation, and what sort of advantages they have to gain (beyond the sheer cinematic glory of it!)
This Colossal Creatures ruleset was forged inside my personal homebrew campaign, heavily inspired by Shadow of the Colossus, Monster Hunter, and my primal obsession with tiny heroes clashing with huge monsters. These rules aren’t finished, and I’ll likely go on tweaking them forever and ever, so I encourage you to keep what you like, change what you will, and drop the rest. Please leave your feedback in the comments too! Together we can help this ruleset evolve into something great.
Despite the wording so-far, these rules can be used for Large monsters, Colossal monster, or anytime a smaller creature wishes to grapple a larger creature. They are even useful for vehicles, moving terrain, and other uncertain footing!
The simplest version of this ruleset revolves around the following terms:
|For the smaller creature (doing the mounting)||For the larger creature (being mounted)|
|Mount Check |
A Strength (Athletics) or Dexterity (Acrobatics) check usually opposed by the Mount DC.
The act of attempting to grapple onto a larger creature.
|Mount DC |
10 + the creature’s Dexterity modifier.
How difficult it is for a smaller creature to mount this creature.
The condition of being grappled to a larger creature.
The simplest way for a creature to rid itself of mounted creatures: a good, hard shake.
What occurs between losing the mounted condition and hitting the floor.
The reward for risking life and limb to mount a creature: weak points offering Advantage and extra damage!
Each of these terms will be expanded upon in the rules to come. They are chosen for clarity’s sake and to serve the flow of combat. A typical turn may look something like this:
Player: I charge up and onto the Giant Snapping Turtle‘s shell…
GM: Okay, make a mount check.
Player: With Athletics it’s a 16.
GM: Alright, you are now mounted on the Turtle… Here.
Player: I climb up further and strike at its neck with my axe!
GM: That definitely sounds like a weak point – roll with Advantage.
Player: It’s a 17.
GM: Hit! Roll an extra d12 damage, and then the Turtle will use its reaction to try and shake you off – make another mount check. The Turtle rolled a… 15.
Player: …It’s a 12.
GM: You’re flung from the Turtle’s back and take… 4 bludgeoning damage from falling. Now it’s the Turtle’s turn…
Optional rules. This ruleset is designed to be robust, yet simple. Consider these grey boxes as optional rules for fringe cases and additional options.
Combat Against Colossal Creatures
Mounting a Creature
Mounting is the close cousin of Grappling, and allows smaller creatures to get an edge on creatures that are significantly larger than them.
The Mount Check
A mount check is made in order to gain or maintain a foothold on a creature that you can traverse. You can attempt to mount a creature that is at least one size larger than you, and doing so costs half of your movement speed.
Even while mounted, certain situations (such as a creature’s Shake action) may force you to repeat your mount check. Whether making an attempt to mount or maintain your mounted condition, the check is the same:
The mount check is a Strength (Athletics) or Dexterity (Acrobatics) roll (you choose the ability to use) and the baseline DC is equal to 10 + the target’s Dexterity modifier. If you succeed, you gain the Mounted condition. If you fail, your movement speed is spent but you suffer no other penalty.
If you have a climb speed, you always make this check with advantage. If the target creature is prone, you can make this check with advantage. You succeed automatically if the target is incapacitated.
If you fail your initial mount check to mount a creature, you are flung off and land prone within 5 feet of the creature in a space of the creature’s choosing.
Landing on a Creature
If you leap from a tall place, approach by flight, or attempt to teleport onto a creature, you may attempt to land on and mount a creature on a space that you can reach at the end of your maneuver.
Landing on a creature requires a successful mount check. This check can be made as part of a spell or ability that teleports you onto the creature.
On a failed check, you immediately begin falling.
The Mounted Condition
While mounted to a creature, you move along with it, and can move within the spaces it occupies. Each foot of movement across the creature costs 1 extra foot. You ignore this extra cost if you have a climbing speed. At the GM’s option, certain surfaces of the creature may be more or less difficult to traverse, either requiring no extra movement or requiring an additional mount check to maintain your footing.
Though a creature only occupies a certain number of horizontal spaces, it is up to the Game Master how tall it is and how much climbing may be required to reach, for example, its shoulders. In most cases, the ‘theatre of the mind’ will suffice, though you may wish to track the altitude of each mounted creature. For especially tall or complex creatures we recommend a separate map depicting a few vertical slices, much like a tower battle map might be separated into multiple levels.
Losing Your Footing
Staying mounted to a creature is tricky business. The following scenarios can end your mounted condition and cause you to fall:
- Willingly. You may end your mounted condition willingly as part of a normal move or jump.
- Taking damage. Like a concentration check, if you take damage while mounted you must succeed on a mount check to maintain the condition. The DC equals 10 or half the damage you take, whichever number is higher. If you are concentrating on a spell, this check should be made after your spell concentration check.
- Being knocked prone or forced to move. If a spell or ability knocks you prone or forces you to move, you must also succeed on a mount check in order to keep your foothold.
If the spell or ability also involves damage, only one mount check (the one with the highest DC) is required.
- Creature Retaliation. Creatures may attempt to grapple, shake, scrape, or otherwise dislodge you.
- Being Incapacitated or killed. You immediately begin falling if you are Incapacitated or if you die.
The Brace Action
When you take the Brace action, you focus entirely on maintaining your foothold. Until the start of your next turn, you make mount checks and Dexterity Saving Throws with advantage. You lose this benefit if you are incapacitated.
You begin ‘falling’ immediately after you unwillingly lose your mounted condition.
Falling is divided into two different stages: Tumbling and Free Fall. This division is optional however, and is useful for making falling more forgiving. If the creature being mounted isn’t sufficiently large or you just want to keep things simple, you can skip the Tumbling stage and treat every fall as a Free Fall. Finally, the Last Grasp optional rule is offered for cases where a fall might result in instant death!
If you are falling, but are still within a space occupied by a creature, you are considered ‘tumbling’; you have lost your foothold and you are rolling or sliding off the creature.
When you first enter a tumbling state, and at the end of each of your turns while you are tumbling, you are forcibly moved 1d4 x 5 feet away from the center of the creature, or in the direction chosen by the Game Master. Movement caused by tumbling does not provoke attacks of opportunity.
During your turn you may spend half your movement to attempt a new mount check. On a successful check you regain your mounted condition and are no longer considered prone or falling.
If you tumble into a space unoccupied by the creature you were formerly mounted to, you immediately enter a free fall.
When you first enter free fall, and at the end of each of your turns while you are in free fall, you instantly descend up to 500 feet.
At the end of a fall you suffer 1d6 bludgeoning damage for every 10 feet you fell, to a maximum of 20d6. You are also knocked prone, unless you avoid taking damage from the fall.
When you enter free fall or fall past a surface that you might plausibly grab hold of, you can spend a Reaction to attempt a Last Grasp.
The Last Grasp is a DC 15 Dexterity Saving Throw. On a success, you immediately stop moving at the edge of the precipice and you regain the mounted condition, but you are still considered prone until you are able to stand up.
The primary purpose of mounting and climbing a creature is to strike at its weak points. These may manifest as a crack in its armor, an area of soft flesh, or some other vulnerability.
Attacking a Weak Point
To target a weak point you must be mounted to the creature and within 5 feet of the weak point you are targeting. Only ranged critical hits can strike weak points from further than 5 feet away, otherwise they must be made at point blank range.
When targeting a weak point, all attacks against the weak point are made with advantage and ignore any resistances that creature may have.
Weak Point Strike
Once per turn, when you score a hit against a weak point, you can roll a number of additional dice chosen by the Game Master and add the total to the damage of the hit.
These extra damage dice represent the vulnerability of a particular weak point. For example, a dragon may suffer 1d8 extra damage to its eye or 3d6 if struck in the missing scale over its heart.
Passive Mount DC
The basic DC to mount a creature is equal to 10 + the target’s Dexterity modifier. In Addition to this, rain, smooth scales, knotted hair, and other factors may influence this DC on a space-by-space basis defined by the Game Master. See Designing a Colossal Creature for more information.
A creature may use the Attack action to make a special melee attack, a ‘shake’. If the creature is able to make multiple attacks with the Attack action, this attack replaces one of them. A creature who is struck in its weak point may also perform a Shake as a reaction.
When the creature performs a shake, all creatures mounted to it must immediately make a new mount check to maintain their foothold. Targets of a shake must succeed on a mount check contested by the creature’s shake check: a Strength (Athletics) or Dexterity (Acrobatics) check (the creature chooses the ability to use).
On a successful check, the target maintains its mounted condition. A target that fails a shake check loses their foothold and begins falling.
If a target is mounted to the creature and also concentrating on a spell, the target must succeed on a concentration check to maintain the spell. This check must be made before the mount check.
A creature can attempt to grapple any creature that is mounted to it that it can reach, at the Game Master’s discretion. If this contest is successful, the target becomes grappled, is no longer mounted, and is moved to an unoccupied space adjacent to the creature (chosen by the creature).
A creature can hurl a target away as an Action if it is grappling the target and the target is one or more sizes smaller than it. This ends the grapple, catapults the target a number of feet away equal to 2d6 x the creature’s Strength modifier (with a minimum of 5 feet) and deals half this amount in fall damage.
A creature can attack any creature that is mounted to it that it can reach, at the Game Master’s discretion. Targets that take damage from such attacks may be dislodged, as per the Taking damage rules in the chapter on Losing Your Footing.
That’s all for now! This ruleset is still a work in progress, and I hope to formalize more and more of my scattered ideas by the week. The rules here already are more than enough to play with, but I am eager to expand upon them below – stay tuned!
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Designing a Colossal Creature
The ruleset above are carefully designed to work in any situation where a smaller creature wishes to grapple and mount a larger creature. What follows are some additional rules to help you in designing creatures and encounters around mounting; encouraging it with critical weak points, discouraging it with slick surfaces, or simply adding more actions to a creature’s repertoire!
Quick Conversions. Existing creatures can be adapted quickly simply by adding a few of the options listed below. For example, you might give a Stone Golem a higher Armor Class but a 2d6 Weak Point in the form of a magical sigil on the back of its neck.
Weak Point Options
See the Weak Points chapter for the rules concerning regular weak points.
Critical Weak Points
Certain weak points, if damaged sufficiently, may rob the creature of one of its abilities. For example, striking the wings of a creature may force it to land, or striking a dragon’s throat may rob it of its breath weapon. You may consider tracking a separate health point pool for these weak points in addition to the regular effects of a weak point.
A creature struck in a Critical Weak Point is likely to use its reaction to perform a shake.
These traits offer a few ideas to add further variety to an encounter with a colossal creature. They might apply to a creature as a whole, or perhaps only certain portions of its body.
- Vigorous Shake. The creature can use the Shake special attack action to affect its entire body, rather than a single zone.
- Smooth Surface. Mount checks on this creature using Strength (Athletics) are made with Disadvantage.
- Unpredictable Movements. Mount checks on this creature using Dexterity (Acrobatics) are made with Disadvantage.
Encounters & Battle Maps
We’ve already created a handful of resources that pair well with these rules, which you can find below:
Crushed Atop the Cliffs – Colossal Crab and Sahuagin Encounter
A group of sahuagin are about to attack a town with the help of a monstrous colossal crab. Can the party stop them and free the crab?
Scorn of the Sands, Part 3: Desert Sled Encounter
The final confrontation between the party and the undead scourge of the desert, K’rhamas. Will their plan succeed or will they join the sled?
26 MAR 2022. Added a penalty for failing the initial mount check; “If you fail your initial mount check to mount a creature, you are flung off and land prone within 5 feet of the creature in a space of the creature’s choosing.” Previously, a character already in melee could attempt two mount checks per turn without any risk besides the cost of their movement.