To-Hit Rolls

To-hit rolls are an RPG mechanic inherited from pen-and-paper systems. They represent an obvious intuition (attacks can miss) and use a binomial mechanic with a random chance. Many non-RPG computer games use a different mechanic: did the sword, shot, spell, or whatever hit the target?

One of the City of Heroes developers remarked that, had he to do it over again, he would not have included a to-hit roll or an accuracy stat. Every attack would hit unless some defense caused it to miss, and then you would have an indicator of why you missed.

The relative merits of damage mitigation versus avoidance are a rich topic, not to be explored here. One note is that the difference really matters when there are secondary effects. If an attack does X damage and blinds you for Y seconds, a miss means neither X nor Y, while a mitigated attack means taking X/z damage and the full blind. You could also have mitigation apply to the blinding, but that is usually handled through another mechanic, such as resistance to burning or quicker debuff recovery.

Accuracy stats facilitate high variance effects. For example, an attack that does 100 damage with 100% accuracy has the same DPS as an attack that does 1000 damage with 10% accuracy. The difference is consistency and the importance of damage spikes. Against a target with 90 hit points, you prefer the reliable attack. Against a target with 100,000 hit points, you are relatively indifferent. Against a target with 500 hit points and 200 points of damage reduction (or that regenerates 100 hit points between your attacks), you prefer the inaccurate attack. (There is a similar spike effect with fast, weak attacks and slow, strong attacks.)

Accuracy rolls are seen in many games, sometimes surprisingly so. First person shooters, for example, often include an accuracy mechanic. Bullets do not necessarily go where your gun points. Sniper rifles usually have pinpoint accuracy while shotguns shoot a cone in a general direction. This is often handled invisibly. Borderlands attaches a specific accuracy stat to each weapon and then accuracy bonuses to characters and abilities; the Mechromancer has many abilities tied to lowering accuracy, and I am not sure that I know what -500% accuracy would mean. (Note: this is not exactly the same mechanic, because it moves the bullet in a semi-random trajectory around the intended target, as opposed to having the bullet reach the target and then give it a chance not to hit anyway. I recall having seen games stack “accuracy” systems where you need both to aim properly and to pass a roll, but examples are not leaping to mind.)

NPCs in FPSes need an accuracy stat because the computer’s default is perfect accuracy. (“I flinch at each shot, because I understand now that every bullet fired is ending a human life. Otherwise SAP wouldn’t have pulled the trigger.” Robopocalypse by Daniel Wilson) If you want to see how that changes the game, see the Scarecrow in Arkham Asylum or Deadshot in Arkham City, both of whom instantly defeat you if you enter their field of vision.

In Dungeons and Dragons, armor classically reduces the chance that you are hit rather than reducing damage; either you hit for full damage or you miss, and damage reduction abilities were added in different forms in different editions. Also classically you have a 5% chance for a lucky hit (and/or critical) and a 5% chance for an unlucky miss (and/or fumble) no matter what. City of Heroes and many D&D-based games kept the auto-hit/miss rolls, down to the 5% chance of each.

City of Heroes added pop-up text to the pop-up damage numbers indicating when defensive abilities mattered. “402 327 Deflect! 239 Deflect! Deflect!” I think demand for Force Field/* Defenders shot up dramatically after that. The Lord of the Rings Online did something similar with block, parry, and evade, and then partial versions of each.

Guild Wars 2 implemented the CoX vision: every attack hit unless it had a reason to miss. There was no inherent miss chance. You could miss by being too far away or because your projectile did not hit the target (obstructed view, darting movement). You could force a miss with the blind condition, the aegis boon, by blocking, or by dodging (some abilities have an equivalent “evade” effect). Indicators of why the misses happened were spotty; you saw messages for blocking, evasion, or obstruction, but a simple “miss” could come from several effects

Some games that do not use accuracy have a few units (or an entire race) with miss chances. Doing so highlights the unreliability of the units in question, and the “miss” chance might be something else entirely: an experimental explosive that is a dud, a race distracted by shiny objects, or some technobabble about quantum mechanics meaning that the attack does not work 50% of the time. If everyone has 90% accuracy, a 30% miss chance does not sound that bad, but when the default is always hitting, any miss chance feels meaningful.

As a player, reliability is usually on your side. Unless a huge damage spike is all that matters, randomness hurts you. This is basic game theory. In an average fight, you win with most of your health and then need a few moments to recover. If your luck is very good, you will kill the monster in fewer attacks, shaving some seconds off the fight and recovery. If your luck is very bad, you die. The monster has the better upside. Refer to the math above: if the monster has 500 hit points, a 100% chance/100 damage attack always wins in 5 attacks, while a 10% chance/1000 damage attack unfavorably combines unreliability with overkill.

On the other hand, players seem to really like overkill and big numbers, and an unlikely string of misses is a chance to complain on the forums.

: Zubon

5 thoughts on “To-Hit Rolls”

  1. Interesting post. I have to feel that the games which implement the 100% accuracy rule, where misses are based on external factors (dodging, obstruction etc) are more my kind of thing because you can plan your attacks better. Plus you don’t get an assassin teleporting to you and hitting you with 10000000 damage because their 5% chance attack skill managed to land. If he hits you for 10000000 damage it is because he legitimately specced to do so (or is a cheating exploiting haXX0r n00b).

  2. Riot’s reasoning for removing dodge from LoL was basically this; it’s unreliable and not fun. You don’t feel heroic when you dodge 1/10 attacks, but the person who misses killing you by one hit because the final shot was dodged feels cheated. You did nothing skill-based to win, the RNG just favored you that time.

    On the MMO front, Darkfall combat feels very player-skill based because the only way to miss an attack is to actually miss it. The game never interfered with things like dodge or homing missile attacks.

  3. The City Of Heroes accuracy comment probably depends rather heavily on context. It’s worth noting this is a game where ‘base’ accuracy is 75% — one hit in four will normally miss — and that players are balanced around taking an average of 8 successful attacks to defeat an enemy, according to game developer posts. ((In practice, this number wildly changes from class to class, but it’s how they discussed design choices back when folk were first figuring out the brawl index.)) Moreover, it isn’t viable to improve accuracy seriously until level 12, and most players did not apply such a focus until level 22, almost half-way through the game, due to how the Enhancement system works, and the game is progression-based (at least as of issue 8, players mostly focused on raising alts).

    That particular combination made the matter particularly significant, and explains why CoH had a number of unusual internal mechanics, such as a ‘streakbreaker’ that forced a player’s next attack to automatically hit after a certain number of misses based on their accuracy, that most other games including other games with To-Hit rolls don’t have forum outcry to implement.

    The fundamental issue is probably that of consequence. To Hit rolls are a Helpless behavior; very few games allow any changes in-combat that dynamically change Accuracy as a stat — it’s either impossible or unfeasible to change enhancements mid-fight or even mid-mission in CoH — and temporary buffs seldom have high uptime or significant effect for the few classes that have them (or by the time they have them, single-origin enhancements make the tohit cap viable).

    Active effects are different; you can pay attention and use weak attacks when you’re affected by a Blind condition and the mob must have used an attack that was less damage-efficient for the sake of having a Blind value (and/or is dependent on a position-dependent field effect, such as a Thief’s Black Powder). Even enemies moving out of range of a melee fighter are exchanging movement time for protection and giving players the choice between closing distance or focusing on ranged attacks. City of Heroes actually had some attributes like this, most obviously for Storm/Darkness Defenders and some other setups, who could use knockback and short-duration significant accuracy debuffs as if they were blinds.

    Of course, from a programmer’s perspective the GW2 model is vastly more difficult than running a couple rnd() routines.

  4. Elder Scrolls: Morrowind (not an MMO, but still) is a game which stacks accuracy systems, if I recall correctly (it has been awhile since I played). With a bow, you have to hit the enemy with an arrow and then you have a chance of the attack failing, while with spells you have to succeed in casting the spell, then actually hit the enemy with it.

    Personally, I’m glad they removed that mechanic in Oblivion. If you succeed in making a stealth shot from halfway across a city, it shouldn’t fail due to some random number generator.

  5. D&D (at least the versions I’m familiar with) also has the saves, where a successful roll often halves damage and/or removes an extra effect like blinding. I guess in MMOs this is often a specific resistance stat to a specific condition type thing. Saves are nice because certain spells and abilities can have their own rules as to what happens on a successful save, and certain classes too (like rogues in Pathfinder taking no damage instead of half damage on a successful reflex save).

    Random miss chances make more sense in pen-and-paper contexts in my opinion, because it’s an abstract simulation; you can narrate any reason for an attack not landing, whether bad luck, good blocking, distraction or whatever. In a video game, it’s less abstract, it’s right in front of you – your actual reflexes are involved, so the randomness can seem unjust.

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