In fantasy fiction, there are really only two kinds of threats in combat: straightforward and serious. This is pretty obvious to spot in movies:
So how can you tell which enemies are serious and which are straightforward?
One way is to see how much screen time they get. When the camera stops long enough that we get a nice look at a brutal enemy, you know it’s going to take more than one slice to take them down.
Another way is to give them a name. Although his name isn’t explicitly said in the movies, that lovely Uruk chap with bad dental hygiene is Lurtz. But you wouldn’t know that from watching the films.
The way that this movie telegraphs the threat of Lurtz is screen-time and dialogue, but just by appearance, you know this guy is the leader and that he’s tougher for it. The title spoils it, but yeah, no helmets.
The phrase “Helmet On, Helmet Off” means that the different enemy in a group of enemies is the leader/most powerful. It’s another way to telegraph threat that is immediately understood (consciously or not) by players.
Now, the “serious threat” enemies may still have a helmet, that’s fine. But their helmet is CLEARLY different from the other helmets. They have the coolest one. Examples include:

All of these villains die without their respective helmets/masks on… Huh. There’s no huge connection here, it’s just something I realized while making this collage.
In Old School games and games that use Diceless Violence anything and anyone can be a threat, so telegraphing the difference between “mooks” and “true monsters” can ease players into feeling awesome before you throw a serious threat at them. It also gives a better pace to large-scale fights, building towards true bosses, instead getting bogged down by a slog of “small potatoes.”
Another use of “Helmet On, Helmet Off” is for players. Again, it’s another way to convey how serious a fight is getting. It shows a clear difference between the initial “warm-up swings” and “this is where the real fight begins.”
The idea for this post actually came from watching Berserk (1997). There are many army-to-army fights in there. And nearly every fight begins with the heroes with helmets on.

Then, at some dramatic moment, when the enemies seize the upper hand, when a brute enters the scene, when things are looking grim, the hero’s helmet comes off. It’s usually shattered by an attack or somehow removed without also taking the wearer’s head clean off with it.

If this were set in an RPG, this would be the GM showing, not telling, the players “buckle up.” So players can enjoy the “combat as sport” romp, getting a few good hits in, having things look cinematic, having the satisfaction of feeling awesome, and then: BOOM. Combat as war. You could die now. Are you ready?
So maybe the GM uses the helmet coming off a signal for players, but what if instead the characters took off their own helmets? I’m thinking of something like this.

And then Eowyn stabs the Witch-King through the face. Excellent scene.
In The One Ring RPG, you actually regain some form of stamina if you take your helmet off during combat. Although here, Eowyn is clearly taking off her helmet for additional damage. I like that. Maybe it’s a one-time effect: “When you take off your helmet during combat, your next hit gains +d12 damage.” Or this could also be fun: “While you have your helmet off, you deal +d8 damage but take an additional +d8 damage.” Insert your dice of choice.
To me, this feels vaguely like shields shall be splintered (Geez, what’s with the LOTR references today!). Using other pieces of gear for mechanical effect can be good. I mean, we use armor for Armor Class and Damage Reduction, why not give other traditional pieces of gear different uses?
So there are some thoughts on helmets for bad guys and good guys.
I’m kind of intrigued by other mechanical ways to use gear to be honest… Another time.
I always fancied having my monsters kick my pcs into breakaway objects to let them know things were serious. Or visa versa!
I love the comparison. Players always seem to need more flags. It reminds me of the ‘named men’ from the First Law series. From a Hollywood perspective, you have face time for the big names at the fancy moments. From the storytelling side, you start with gear – this is your ability to scheme and cover yourself with munchkin level layers of impressiveness. Then phase two is where the beast is unleashed, and your ruined armor is cast aside for a true fight based on ability alone. Also, dehelmeting seems symbolic like a haircut, complete with ‘Now you’ve made me angry’ face.
I love thinking of mechanics like these, not that I am good at it.
“When you tell others to go away, and that you will handle the enemy alone, risking death, you get .”
“When you finally choose to accept someone who you didn’t like and fight alongside them, you both get a .”
“When you look at some item from back home and remind yourself of where you came from, you get .”
Also, not sure about others, but I much prefer the first helmet example, the ‘when’ one. The second one, the ‘while’ one, feels meh. Maybe I play too many pbta games.
I added a new helmet rule for 5e dnd due to this post, and my group loved it:
While wearing a helmet, gain +1 AC but suffer -1 to attack rolls and spell DC.
When you remove the helmet and throw it to the ground for dramatic effect, then hit with an attack immediately after, that attack deals 1 extra damage per character level.