Rules Lab: Knockdown

n.b. The Rules Lab feature presents house rules and variants I am currently using in my D&D games or that I once used and am now experimentally updating for 5E. Today’s presentation of a system for knockdown is the latter. Special thanks to Eric Stefen for his help with these rules.

Sometimes I miss when my group used rules for the possibility of being knocked down during combat.

I don’t mean someone using the “Push” action to knock someone prone, but rather a system wherein almost every successful blow had at least some chance of knocking down an opponent.

Soon after I joined up with a group of gamers when I transferred college in the mid-90s, I began to incorporate various tactical rules into my D&D games based on supplements being used by other DMs in my network. This included the use of miniatures and a battlemat and making use of many of the proto-3E rules found in the Player’s Options books that many people refer to as 2.5E.

Rollo Snow knocks down a Troglodyte Mystic the old-fashioned way, by bringing it to 0 hps.

I love tactical combat. But even more, I love the random elements and unexpected outcomes in combat that reinforce or foil strategies and lead to new tactics. I want combat to be more tense, more fun, more spontaneous, and while I would hesitate to say “realistic” (little to nothing about D&D is “realistic”) I still like simulating the chaos of battle. “Fog of war” is a phrase that is spoken around my tables a lot to explain the strange outcomes and critical fumbles that led to hitting an ally, breaking your sword, or stumbling from the force of a blow and sliding head-first down a gravelly embankment.

That last possibility of falling to the weight of the blows against your armor, against your shield, against your head, from desperately trying to avoid being brained, or from the pain of a spear blow to your side is what the knockdown rules I incorporated were meant to simulate. While the knockdown rules add-on may seem a little kludgy in relation to 5E’s relatively smooth mechanics (being an add-on to every attack roll and some spells), it worked well throughout our time playing 3E and I have no reason to believe that would not be the case for 5E with some tweaking, that is: once the players get used to it.

It is not that I think these rules are all that complex (though they do seem kinda bananas while looked at in aggregate). It is just that they are different from what most people are used to. They are so simple in fact, that despite (regretfully) getting rid of my copies of the Player’s Options books during one of my RPG purges, I still remember exactly how the rules worked, most of the numbers associated with weapon type and creature size that went along with them, and could quickly figure out what I don’t remember at the moment. That said, what I remember is how we implemented the knockdown rule, not necessarily what was printed in the book that inspired that implementation.

Does this rules add-on complicate combat? Yes.

Does it add significantly more dice rolling and another set of things to remember with normal combat rolls? Yes.

Is it a perfect system? No, it isn’t. Some weapons become just straight up better than others and some weapons break the rule of thumb (shared below) for determining its chance to knockdown (crossbows, war pick, and whip being examples). As such, it is not always easy to remember off the top of your head which die to use for a particular weapon (though that is more on the DM than the players, the latter of which should have it marked down next to their weapons). It also calls on the DM to adjudicate what the knockdown die is for the various natural weapon attacks of a whole lot of monsters. Furthermore, since the DC for the saving throw against knockdown is modified by Strength and either Strength or Dexterity are used to save against it, this rules add-on raises the value of both ability scores, which many consider to already be overvalued. This is especially true of Strength since it is used to determine the save DC even when using a ranged or finesse weapon. And, lastly, sometimes a weapon’s chance to knockdown an opponent is just not gonna matter. There is no way, for example (short of special feats or magical weapons), for an arrow fired from a shortbow to ever knockdown an ogre.

Is it worth it? Only you can decide that, but I can say that in the games where we used knockdown it added another layer of excitement to combat as the players both had to deal with the consequences of being knocked down and the pleasure and opportunity of knocking down opponents. I will also say, however, these rules are most effective when used along with another house rule we instituted wherein standing from prone drew an attack of opportunity. The way we parsed it in 3E was like this: standing from prone as a move-equivalent action drew an opportunity attack. Standing as a standard action represented a more defensive attempt to stand and did not. I have included a 5E equivalent with the rules of knockdown below.

What is presented here is experimental (I hope obviously so), and I encourage anyone interested in implementing these rules to play with them and let me know what they come up with and if they actually use them to reach out and let me know how it goes. And for the sake of full disclosure, I have not and likely won’t be implementing these rules in my own 5E game or even the 5E clone I am currently working on.

One last thing before I go on to explain how knockdown works: My group was the type where everyone rolled multiple dice at once and were encouraged to do so by the table culture. Thus for example, in 3E where you had to roll a second d20 to confirm critical hits, for every attack players rolled two d20s of different colors to differentiate the attack roll from the potential crit (or in our case, fumble) confirmation, the damage die (in case you were successful in the attack), and the knockdown die. So at least four dice were rolled at once every time, though you only had to look at the attack roll d20 to see if the others were necessary. This sped things along quite a bit. Our combats rarely, if ever, slogged, though that also has to do with the way I run combat (which I will be writing about soon). I think one of the reasons this worked is because in my experience, players like to roll dice!

For a bunch of narrative examples of these knockdown rules in use check out the “Out of the Frying Pan” story hour.

Below are the detailed rules for this combat option, followed by a link to a PDF version for easy printing.

Knockdown Explained

The opportunity to knock down an opponent accompanies every successful attack roll. Whenever you strike an opponent—or an opponent strikes you—there is a chance the target is knocked prone by the force, weight, and pain of the blow which is determined by the knockdown die associated with the weapon or attack type used. Thus, for example, when striking with a mace—which has a d8 knockdown die—you’d roll a d8 along with your normal d20 attack die and separate from its d6 damage die.

These knockdown rules make use of non-standard polyhedral dice, such as the d14, the d16, and the d24. While such dice do not come in the standard set, they are available at many gaming stores and online as other games (such as the excellent Dungeon Crawl Classics) make use of them. In addition, most die-rolling apps (like the ones used on Discord ) allow for simulating the rolling of these dice.

Every creature has a Knockdown Threshold number determined by its size (see table on right). If the result of the attack type’s knockdown die matches or surpasses a creature’s Knockdown Threshold, the creature struck must make their choice of a Dexterity or Strength saving throw (DC = 8 + Strength modifier + proficiency bonus) or fall prone. The DC is modified by Strength even when the weapon being used is usually modified by Dexterity like ranged or finesse weapons. Crossbows, due to their mechanical nature, are the only exception. In their case they use a bonus of +0, +1, and +2 for hand, light, and heavy crossbows respectively instead of the attacker’s Strength modifier. A second level fighter (+2 PB) with a strength of 12 (+1 modifier) would make the DC for his successful knockdown rolls an 11. The proficiency bonus does not apply if the attacker is not proficient with the weapon they are using.

Creatures with more than two legs or that can fly make this saving throw with advantage.

The Knockdown Die: The knockdown dice are: d3, d4, d6, d8, d10, d12, d14, d16, d20, d24, d30.

The knockdown die for a weapon usually adheres to the following guidelines: slashing weapons use a knockdown die equal to the size of their damage die, piercing weapons use a die size one lower than their damage die, and bludgeoning weapons use a die size one higher than their damage die.

There are a few weapons that are exceptions. Weapons that use two dice for damage (like the maul’s 2d6) should use a die equal to the maximum possible damage (in this case d12) as the base which is then modified by the type of damage it deals (thus, the maul goes up to a d14 knockdown die). The knockdown die of versatile weapons is different when used one- or two-handed.

The knockdown die is never modified by any ability score. Nor is it (or the save DC against knockdown) ever modified by the “plus” of a magical weapon unless that magical weapon was specifically designed to have that additional effect. I would be cautious in increasing any weapon or item’s knockdown chance too much by granting magical items a knockdown bonus.

Getting Up: The optional knockdown rules also modify how getting up from prone functions in 5E combat. Now, getting up allows any opponent within reach to use a reaction to make an opportunity attack. Remember, attacks made against prone targets are made with advantage. Using the Disengage action along with half your movement obviates the opportunity attack for standing up (even if you don’t move away).


Multiattack & Dual-Wielding

When a monster or player character has multiple attacks on the same turn, the knockdown die is rolled with every successful attack. As soon as one of the attacks successfully knocks down the opponent, there is no need to keep rolling to see if the others achieve a knockdown. Note that creatures and characters with multiple attacks can knockdown an opponent with one and then benefit from Advantage with subsequent attacks on the same turn, since each one is declared separately after the result has been determined.

Lastly, when determining the save DC for a knockdown from an off-hand weapon, the Strength modifier is not added unless the attacker has the two-weapon fighting ability or the dual-wielding feat.

Monsters (& Unarmed Attacks)

When it comes to monster attacks, the DM should make a ruling as to what knockdown die makes most sense using the guideline below. Of course, when monsters use weapons simply use the knockdown die of the weapon they are using but when relevant, modify it by size (see below).

The base monster-attack knockdown die is determined by the damage die it uses. It goes down a step for Tiny creatures and goes up a step for each size category above Medium (thus one step for Large, two for Huge and three steps for Gargantuan). When a monster’s attack damage uses multiples of a die, like 2d8 or 3d6, modify the base die type as follows: apply the modifier for the damage type and creature size (if applicable) and then increase die type a number of steps equal to the number of dice after the first. So using the examples above, an attack that deals 2d8 bludgeoning damage would have a knockdown die of d12 (d8 +1 step to d10 for bludgeoning and a +1 step for the extra die). In the case of an attack doing 3d6 piercing damage the knockdown number would be d8 (d6 -1 step for piercing, +2 steps for the extra dice). However, you should also consider the type of attack and adjust up or down as feels necessary. For example, a monster with sharp chitinous tendrils that whip at opponents might have a higher knockdown die for those attacks even if they do slashing damage, since the whipping action is intuitively more likely to knock or pull someone off their feet.

Attacks that already have a mechanism for knocking opponents prone (like the Air Elemental’s whirlwind, a dire wolf’s bite, or a lion’s claw attack as part of a pounce), should be left as is and not have an additional chance of knockdown.

It seems like an unnecessary effort to go through and rate every single monster’s every single attack ahead of time. Instead, I recommend just making a note of it when preparing a specific encounter. That said, l give a few examples for some common 5E monsters below.

Spell Knockdown

Figuring out the knockdown die for spells uses the same basic guideline as weapons and monster attacks. The knockdown for spells is based on damage die and then adjusted based on the damage type. Furthermore, the die type is raised an additional step for every 5 full damage dice. Spells that already have a chance to knock targets prone should not get an additional knockdown chance. When determining the DC against being knocked down, use the spell caster’s ability score modifier in place of Strength.


Now that the rules have been laid out, let’s look at an example (though an example feat working with these rules follows):

Rastfar Buhrad-Puhn, the 7th level dwarven fighter 2/cleric 5 with a Strength of 20, is using a maul in his battle against a band of hobgoblin soldiers.

Rastfar’s dice (clockwise from the left). A d20 for the attack roll, a d14 for the knockdown chance, and a d12 for damage.

On a successful hit, he rolls his knockdown die along with his damage. The knockdown die for a maul is a d14. He rolls a ten, which surpasses the knockdown target for a medium creature. In addition to the damage she normally takes, the hobgoblin must make a Dexterity saving throw against DC 16 (8 + 5 [strength modifier] +3 [proficiency bonus]). The Hobgoblin has a +0 to his Dexterity saves, so the DM decides to use Strength (a 13) instead, which gives the hobgoblin a +1, and rolls a 13 for a total of 14. The hobgoblin immediately falls prone.

On the hobgoblin’s turn, she may use half her movement to get up as normal in order to attack, allowing Rastfar (and any other enemies within reach) an opportunity attack (with Advantage), or the hobgoblin may take the Disengage action, use half her speed to stand, and remove the opening for Rastfar or anyone else to use a Reaction to get an opportunity attack on her for doing so, but losing the chance to take an attack action in the process.

Let’s look at another example:

Memphis the fey-touched rogue is attacked by a halfling bandit with a short sword and a Strength score of 9. Since the short sword has a d6 knockdown, the halfling has no chance of knocking down Memphis even if he hits. Since he needs to roll at least a 7 to have a chance to knock the Medium-sized adventurer down, there is no point in rolling the die.

If the halfling were attacking Geigy Silvergarn the gnome illusionist/rogue and hit, however, a roll of 5 or better on the knockdown die would have a chance of knocking down the gnome, since he is Small-sized. In that case, Geigy would make a Dexterity save against DC 9 (8 – 1 [Strength modifier] + 2 [proficiency bonus]).

Later that same round, the bandit’s trained owlbear attacks Memphis. It hits with both its claw and bite attacks. The DM rolls the owlbear’s knockdown dice for each of its successful attacks: d12 for its claws and d10 for its beak. The first KD die (for the claws) comes up a 9, meaning Memphis must make a Dexterity (or Strength) saving throw against DC 15 or fall prone. If the save is successful, he will continue to make saves against any subsequent attacks that match or exceeds the Knockdown Threshold for a medium creature. If Memphis were knocked down by the first attack, you no longer need to roll the knockdown die but the remaining attacks are made with advantage.

Finally, below is a feat that could be useful for a build that wants to focus on Knockdown. Originally, this was two different feats, but since 5E feats seem to be across-the-board more powerful than feats in 3.xE I decided to combine them into Knockdown Specialist.

Click here to download a PDF of these knockdown rules.

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