Probably the most popular types of dice mechanic in RPGs would be:
2) Find a target number, add modifiers, roll a dice, add modifiers, compare modified target number to modified dice roll
I've previously posted about some of my ideas around less math, different dice game mechanics, and in general I find the idea of changing the way the mechanic works a bit more interesting than just adjusting the target number or modifiers (aka Math). I like the idea that a player who's character is attacking with a volley of missiles would roll a lot of dice, where as one with a single powerful canon might roll a single large dice. I think that the kind of dice, number, and way in which they're rolled helps give a feel for the action taking place in the game world. Just the sensory experience of seeing the dice, and hearing the sound they make (lots of dice tumbling through a dice tower can sound a bit like a machine gun) help shape the way the game "feels".
Which brings us to the Holtzman Shield Generator!
After posting about the Bene Gesserit Sisterhood the other day I've been listening to the Dune Soundtrack and watching some clips from the movie. One of my favourite effects from the David Lynch film was the look for the personal shields.
The shield blocks fast moving objects, like projectiles or fast strikes with melee weapons, but allows slow moving objects like air or a slow blade to penetrate. What a great concept, and interesting way to make hand-to-hand combat a relevant part of a high technology world.
The challenge is how to represent that with an interesting game mechanic. Adding a bonus to AC, or providing some sort of saving throw would be pretty straight forward, but it doesn't feel very "special" or suggest the unique way in which the device works.
What I've thought up is matching "move slow" which seems counter-intuitive compared to regular combat with "roll low" which is also the opposite of what you're normally hoping to do.
Holtzman Shield Generator
A protective field produced from Phase One of the suspensor-nullification effect of a Holtzman generator will permit entry only to objects moving at slow speeds.
Ranged attacks do not affect an opponent with a shield. A melee attack roll must be lower than that of the opponent with the shield or the attack is deflected.
So if two combatants have personal shields they would need to roll high enough to hit their opponent, but lower than what their opponent has rolled. This puts a skilled fighter (with a lower "to-hit" number) at a considerable advantage over their opponent.
If I were going to use this item in a game I'd add in more details about how it is affected by magic, how long it runs before needing recharging and so on.
Update
Thinking about this some more I want to add something that encourages players to pick knives over great-swords when fighting with personal shields.
I thought about making the damage roll need to be lower (as well or instead of), but that would only encourage you to not pick a larger weapon that your opponent. Instead I think a simple 'less than X' for damage would work best.
Holtzman Shield Generator
A protective field produced from Phase One of the suspensor-nullification effect of a Holtzman generator will permit entry only to objects moving at slow speeds.
Ranged attacks do not affect an opponent with a shield. A melee attack roll must be lower than that of the opponent with the shield, and they must roll 4 or less for stamina loss or the attack is deflected.
Now in addition to wanting to roll lower than your opponent with your attack, you preferably want to use a weapon that doesn't roll higher than d4 for damage. A Knife is a better choice than a Sword which would be deflected an additional 50% of the time.
If you're using a system where characters can use any weapon but they only roll up to a certain dice size for them (like our Weird West game), I'd have the player roll the full dice size when fighting against a personal shield user.
