This is an optional rule for Bold Against Monsters (BAM).
Also, heroic actions can replace Weapon Masteries in D&D 5.5 or Weapon Actions in ToV.
There are also Tips for the GM that might be useful when running any RPG.

In a combat round your character can move and take an action (or move twice if you don’t take an action). The core rules say, “Your action can be anything that your character can do, or attempt to do, that would normally take no more than 6 seconds.” And goes on to describe the “Attack Action” and the “Magic Action” – the two most common actions.

The “your character can do anything” rule may be intimidating to players, and GMs as well. So here a few examples of things the PCs can attempt and rules for succeeding. I’m calling these “Heroic Actions.”

Any player character can attempt a heroic action. Heroic actions do not do damage per se but may cause damage to be done as a result – dependent on environment or impact – so pushing someone off a cliff doesn’t do damage … it’s the fall that does it! If a heroic action forces a target creature into damaging terrain, such as lava or off a cliff, it can make a STR or DEX (target’s choice) save to avoid the move.

Performing a heroic action.
To perform a heroic action requires making an ability check. First name what you intend to do and the effect you want to achieve. Like all other ability checks, the GM chooses the relevant ability and the target number, called a difficulty class (DC). To make an ability check, roll 1d20 and add the relevant ability modifier. If this is something you are proficient at you also add your proficiency bonus (PB). If the total is equal to or greater than the DC, you succeed; otherwise, you fail.

When characters succeed in performing a heroic action with a weapon, rather than doing damage they use the weapon to perform some other function as described.

The guide-lines that follow are only a few examples of how heroic actions are to be resolved. Creative players will certainly come up with new heroic actions.

DISARM
(Unarmed) 
   You must have at least one hand free. You specify which weapon, shield, or object you are attempting to make the target creature drop. Make a STR or DEX check (you decide which), adding your PB to the roll. The DC of the ability check is the AC of the target creature. You make the check with disadvantage.
(With a light melee weapon)
   Select a weapon, shield, or object the target is holding. Make an attack roll against the target with a light melee weapon that you are proficient with. You make the attack roll with disadvantage.
(On a success)
    The target drops the item. The item lands in an unoccupied space, chosen by you, within 5 feet of the target. If no unoccupied space is within range, it lands at the target’s feet.

GRAPPLE
(Unarmed)
    You must have at least one hand free. Against a large or smaller creature, make a STR check, adding your PB to the roll. The DC of the ability check is the AC of the target creature.
(On a success)
    The target must succeed on a STR or DEX save (it chooses which), or it has the Grappled condition. The DC for the saving throw and any escape attempts equals 8 plus your STR modifier + your PB.
(Ending a Grapple)
    A Grappled creature can use its action to make a STR or DEX check against the grapple’s escape DC. It also ends if you are incapacitated. You can release the target at any time (no action required).
PUSHBACK
(Unarmed or with a shield)
    You must have at least one hand free or be wielding a shield. Make a STR check, adding your PB to the roll. You make the check with disadvantage unless you first move 20 feet in a straight line up to the creature. The DC of the ability check is the AC of the target creature.
(With a heavy melee weapon)
    Make an attack roll with a heavy melee weapon that you are proficient with, against a large or smaller creature. You make the attack roll with disadvantage.
(On a success)
    You push the creature up to 10 feet straight away from you.

TRIP OR THROW
(Unarmed)
    You must have at least one hand free. Against a large or smaller creature, male a STR or DEX check (you decide which), adding your PB to the roll. The DC of the ability check is the AC of the target creature.
(With a long melee weapon)
    Make an attack roll with a long melee weaponthat you are proficient with, against a large or smaller creature. You make the attack roll with disadvantage.
(On a success)
    The target falls prone. If the target is mounted, it can make a STR or DEX (target’s choice) save to avoid falling prone.

Tips for the GM:

How to handle it when a player wants to do something not covered in the rules.
What if a player wants his character to swinging on a chandelier, jump onto the back of a monster or throw sand in an opponent’s eyes? Game Masters (GMs) have to quickly respond to these and many other unique situations that crop up all of the time in any RPG. This is a skill that GMs develop with experience. For new GMs, or anyone who would appreciate a few pointers, this will walk you through my thought process when faced with unexpected player requests.

Have the player describe the action and what they expect it to accomplish.

This does two things.
First, it makes the player visualize the current situation and its environment.
     Would the action even be possible for the character to do? If not, it is part of your job to occasionally say no to a player. You should explain to the player why the action is impossible. Example: If they want to jump over a pit of lava that is 200 feet wide. Without flight or any kind of magical assistance, this will be impossible.
     Might it be possible if the rules were loosened? If they could “almost” do it, but the rules don’t allow it, you may want to make an exception in this specific case. It should require an ability check. Example: If they can jump over a 10 foot wide pit and the lava pit is 15 feet wide, I might allow a DC 15 STR check to succeed, but with a dire warning of the consequences of failing the attempt (you fall into the lava pit and take appropriate damage).
     How exactly will they do it? You may need to have the player explain how the character intends to accomplish what he is wanting to do. I find that the player is often thinking that all their character needs to do to accomplish something is to roll a high enough number on the die. By describing exactly how their character will do it, they often realize that they don’t have any way to accomplish their goal. Example: The player says, “While the others are fighting the monster, I run over to the coffin and remove its lid.” Depending on the specifics of the adventure, you might just describe what happens when he opens the coffin. If they haven’t examined the coffin or you haven’t described it, it might be made of stone and the lid is too heavy for a single PC to remove it. The lid may have been sealed by lead or gold. The coffin may be made of wood and the lid may be nailed shut. Another Example: The action may require a tool that the PC doesn’t possess. Maybe they could remove the lid if they had a crowbar. Does the character have what is needed and maybe the proficiency needed to accomplish the intended action?

Second, it gives you, the GM, a little time to decide how to handle the request.

Setting the difficulty.
Always remember, you set the DC and can also require the check to be made with advantage or disadvantage.
If they must succeed: If it is important to the story that they succeed, don’t ask for a check. Regardless of how easy you make it, they might fail (it has happened to me!)
If they must fail: If it would ruin the story if they do succeed, you must resist the temptation to make it too hard for them. Regardless of the difficulty, they may succeed! It will be much better if you don’t allow a check and just say that they can’t do it. If you make it impossible for them to succeed on a natural 20, then why are you letting them roll at all?

     If you feel that you must allow them a chance to succeed, be prepared for them to roll a natural 20. You must allow a natural 20 to succeed. If you allowed them to roll for it, they must have a chance to succeed or what is the point in rolling?  

The following rules apply to “unique” actions.

1.    A unique action will be your action for a combat round but it can also include some or all of your move for the round.
2.    You must describe the action before you roll.
3.    The action must be within the reasonable ability of your character to perform, as decided by your GM, given the character’s level and the difficulty of the action.
4.    If the action is approved by the GM, they will determine the DC and the result of success or failure.
5.    If you roll a natural 1 your attempt fails regardless of any bonuses.
6.    A natural 20 is always a success.

Here are a couple of example unique actions.

Action: “I want to swing on the chandelier and land on the ogre’s back.”
If the proposed action can’t be done, explain why not. But for this example let’s say that it is possible. You could always say something like, “Make a DC15 DEX check, if you fail you land prone at the ogre’s feet, if you succeed you are on his back.”     Or you could make it more interesting. First, you need to visualize the physical layout of the room in 3 dimensions and the location of all the actors. To keep it simple, let’s say this is a large room with a chandelier hanging in the center of the room. It is hanging 10 feet above the floor from a chain attached to the ceiling high above. There is an open staircase on the side of the room with a landing 15 feet above the floor. Let’s also say that the chandelier would reach just above the handrail on the landing, if it were pulled over there. You might say that the character can’t just jump over and grab the chandelier where it is hanging, or if they did they wouldn’t make it swing very far, not far enough to reach the ogre on the other side of the room. For now, we will assume the chandelier is well made and could support the character’s weight. Remember we have already made the assumption that this action is possible. So, assuming the character is standing on the landing, you might ask, “How are you going to move the chandelier over to where you can grab it?”      There may be several different options here. He, or another character may have some magic spell they could cast to move the chandelier. He might say he will use his whip, or make a lasso out of his rope and pull it over that way. Most options for retrieving the chandelier will use his action this round, and may also require an ability check.      Let’s say at the start of his next round he has retrieved the chandelier and is ready to swing across the room and land on the ogre’s back. When he describes exactly how he will do this, he realizes (perhaps with some prompting from you) that he must have both hands free to hold the chandelier. If you are feeling generous, you may allow him to stow his shield and sheath his sword as part of this action. Where the chandelier is now, the center of the room and the ogre should form a straight line. You, as the GM, could dismiss with this requirement, especially if you are playing a more theater of the mind kind of game. That leaves, how does the character land on the ogre’s back and what happens if he fails? I wouldn’t make it too hard, perhaps a DC 10 DEX check to land on the ogre’s back without falling off. If he fails the check he falls prone within 5 feet of the ogre and takes 1d6 points of damage. At the end of his turn he will either be prone at the ogre’s feet, or hanging on to the ogres back. Either way he is holding no weapon and no shield. But if he succeeds, I would reward him for his creativity by giving him one luck point. And, if he is now on the ogre’s back I would give him advantage on melee attacks he makes against the ogre, and give the ogre disadvantage on attacks against the character. I might add that at the start of each of the characters turns, he must make a STR check to remain on the ogre’s back (The GM sets the DC, maybe 15). I might allow the ogre to use his action to attempt to remove the character from his back. This would be a good place to use a contest comparing a STR check from the ogre to a STR or DEX (player’s choice) check from the character.

You might make different decisions, but the point is that you and the player really need to take a minute to visualize, and analyze the situation. What would it look like if you were actually there? Base your decisions on that and you will do fine. Everyone will have fun.

Action: I want to throw sand in the assassin’s eyes.
You could always say something like, “Make a DEX check, adding your PB to the roll. The DC of the check is 8 + the DEX modifier of the target creature. On a success the target is blinded until the end of your next turn.” This would be good if their response to your request to “Describe the action and what you want to accomplish.” Was something like, “The assassin just knocked me prone and you said that the ground there was sandy. I try to keep the assassin from noticing that I close my fist around a handful of sand. As I stand up I fling the sand into his face, trying to blind him.”     Or, if the player didn’t make it so easy for you, you could still just make it a DEX check, or there are several things you may want to consider.

• You can’t throw a handful of sand very far, so I think the target would need to be within 5 feet of the character.
• Also, you would have to be unaware that someone is about to throw sand in your face, or you would instinctively block against it. So the player needs to indicate that he is attempting to be stealthy. Even if they do, you may want them to make a stealth check opposed by the targets perception check for the target to not notice the handful of sand about to be flung in their face.
• Preventing sand from going into your eyes is relatively easy. You could turn away; block it with your hand, arm or shield; close your eyes; or all three. So I would either make the DC relatively high, have the PC make the check with disadvantage, or give the target a DEX save to avoid bring blinded.

As you see, there is always a balance between a fast, easy to play game and one that takes longer but is more “realistic.” The decision is up to you as the GM. The trick is to be consistent. Don’t make it easy for one player but more complicated for another player. And don’t get bogged down in all the numbers and the physics of reality. It’s a game, not a physics class. In the end, most of the decisions you make will, in the end, only add or subtract a few numbers from the die roll, and there are a lot of numbers on a 20 sided die. The big secret is that, no matter what ruling the GM makes, it won’t really make much difference! So, if there isn’t a rule for something, make one up! If you feel it is an important rule, make a note of it and, before the next gaming session, do some research and see if you feel a need to change the rule you just made. White that down and tell the group at the beginning of the next gaming session.

Let me know what you think in the comments below .