Attacking

Basic attacking
If you have sufficient ammo in your weapon and there is a target you have line of sight to within range, you can try to shoot them. Here’s how.

First, to-hit roll:

(Aim + Range + Misc Modifiers) - (Target Defense+Cover) = Target Number

If the roll is within 10 points (above or below) the target number, you inflict a graze. Think of a graze as an anti-crit. It downgrades a standard hit to only doing half damage (rounded down). This is referred to as the “graze band”. Rolls below the graze band are unqualified hits, rolls above it are complete misses.

Now, there are two more rolls to determine damage (they go quick, they’re simple, and it’s on the judge to do instead of you, so don’t worry. Plus, several attacks don't even use these extra rolls, so just chill, alright?!)

Lethality roll: If your attack has a lethality score (by default, most attacks’ score is 0), either because of your weapon or class ability or attacking an exposed target, you simply roll against your Lethality score. If the opponent has a negative dodge score, that counts as a bonus to the Lethality roll.

Dodge roll: If the target has a dodge stat, they simply try to roll equal to or less than their score. If the dodge stat is negative, see above re: Lethality.

If the Lethality roll is a success, it upgrades the type of hit that is made. A miss becomes a graze, a graze becomes a standard hit, and a standard hit becomes a critical hit. Critical hits usually do 50% more damage, but it differs by weapon.

If the Dodge roll is a success, it downgrades the hit much the same way a successful Lethality roll upgrades it. If both the Dodge and Lethality rolls are successful, they cancel each other out.

Range:
Different weapons have different aim bonuses and penalties depending on the distance to the target. Some, like shotguns, have major bonuses up close with severe penalties at a distance. Sniper rifles, on the other hand, suffer no long range penalties but are cumbersome when used in close quarters. Specific range bonuses for different weapons can be found on the Equipment page. They all use the same range increments, however, as follows:

Point Blank - adjacent, can touch

Short - up to 5 paces away

Medium - 6-10 paces away

Long - 10-15 paces away

Cover
The primary method soldiers use on the battlefield to reduce their chances of being hit is to stand behind something durable. Standing adjacent to a cover-providing object gives you a defense bonus against all attacks that cross the plane perpendicular to your point of contact with the cover. “What the fuck, Mike, seriously? Geometry?”  Here, have some pictures: the blue area indicates regions against which the cover bonus applies, and the red indicates angles to which the soldier is exposed. In the second image, no benefit is gained from the piece of cover to which the soldier is not adjacent. In the Third image you see the benefit of an internal corner providing cover in two different axes.

The amount a defensive bonus a piece of cover provides is broken down into two classes: Partial and Full.

Partial (need to crouch behind, or is particularly thin): +20 defense

Full (can stand behind, solid): +40 defense

You can benefit from two different kinds of cover simultaneously. Let’s say, in the third image, the horizontal barrier represented a slatted fence (partial) while the vertical represented a solid wall (full). An attack from the right 2 quadrants would benefit from the full cover of the wall. Meanwhile anything in the top-left quadrant, while technically bypassing the wall, still is protected against by the partial cover of the fence.

Bypassing Cover
Shooting at a target from within their “red zone” or un-covered angles is the simplest way to bypass their cover. There are a couple other fringe scenarios when this isn’t the most hard and fast rule, usually when dealing in close-quarters.

In Fig. 1, soldier A benefits from shooting around the corner to which they are adjacent. They benefit from cover vs soldier B. On the other hand, soldier B does NOT have cover from soldier A in this case.

In Fig. 2, both soldiers are adjacent at the corner firing at one another. NEITHER has cover vs the other.

In Fig. 3, both soldiers are adjacent to one another, firing across a barrier that is fully between them. BOTH have cover vs the other.

Height Advantage
When attacking from a significantly higher vantage point than your target (judge's discretion, but likely a minimum 2 meters) you gain a bonus of +10 to your Aim for the attack.

Reaction Fire
Reaction fire represents a soldier preparing themselves to fire upon an enemy when a certain condition is met. The most common form of reaction fire is the Overwatch action, which grants a single reaction fire attack at the first target that moves within their line of sight. Other abilities grant reaction fire under different circumstances - namely suppressing fire grants reaction fire only against the suppressed target, while other class perks grant reaction fire when characters move within a certain distance, or in response to target behaviors other than movement.

The primary distinction fo reaction fire is that it has an independent 30% miss chance. Before the attack roll is made, a separate roll against a 30% failure is made. If that roll is successful (70 or lower) then the attack roll commences as usual. If the 30% miss chance is a failure, then no attack roll need be made but a unit of ammo is still expended from the firing weapon. If a unit is moving out of cover, they do not benefit from said cover during reaction fire.

If the target is "Dashing", or taking 2 move actions without stopping in between, it increases the miss chace to 40%