First Strike and Double Strike

Overview

First Strike and Double Strike are two of the most important keyword abilities in Magic: The Gathering that modify how creatures deal combat damage. They create a special combat damage step that occurs before the regular combat damage step.

First Strike

First Strike allows creatures to deal combat damage before creatures without First Strike.

Rules

Creatures with First Strike deal damage in the "first strike combat damage step" which happens before the regular combat damage step
Creatures without First Strike or Double Strike don't deal or receive combat damage in this step
If no creatures with First Strike or Double Strike are involved in combat, this step is skipped entirely
First Strike doesn't provide any additional advantage in creature-to-creature combat outside of combat damage timing

Implementation

#![allow(unused)]
fn main() {
#[derive(Component)]
pub struct FirstStrike;

pub fn handle_first_strike_damage(
    combat_state: Res<CombatState>,
    creatures: Query<(Entity, &Creature, &Attack, &BlockedBy, Option<&FirstStrike>, Option<&DoubleStrike>)>,
    mut health: Query<&mut Health>,
    mut damage_events: EventWriter<DamageEvent>,
) {
    // Identify creatures with First Strike or Double Strike
    let first_strikers = creatures.iter()
        .filter(|(_, _, _, _, first_strike, double_strike)| 
            first_strike.is_some() || double_strike.is_some());
            
    // Process First Strike damage
    for (entity, creature, attack, blocked_by, _, _) in first_strikers {
        // Calculate and assign damage
        // ...
    }
}
}

Double Strike

Double Strike combines the benefits of First Strike with the ability to deal damage again in the regular combat damage step.

Rules

Creatures with Double Strike deal combat damage in both the first strike combat damage step AND the regular combat damage step
This effectively allows them to deal twice their power in damage during combat
If a Double Strike creature is removed from combat after the first strike step (e.g., by being destroyed), it won't deal damage in the regular step
Double Strike doesn't increase the amount of damage dealt in each individual step - it allows the creature to deal damage in both steps

Implementation

#![allow(unused)]
fn main() {
#[derive(Component)]
pub struct DoubleStrike;

pub fn handle_regular_combat_damage(
    combat_state: Res<CombatState>,
    creatures: Query<(Entity, &Creature, &Attack, &BlockedBy, Option<&DoubleStrike>)>,
    mut health: Query<&mut Health>,
    mut damage_events: EventWriter<DamageEvent>,
) {
    // Process Regular Combat Damage
    for (entity, creature, attack, blocked_by, _) in creatures.iter() {
        // All creatures without First Strike always deal damage here
        // Creatures with Double Strike also deal damage here
        // ...
    }
}
}

Interactions with Other Abilities

First Strike and Double Strike interact with other combat abilities in specific ways:

Deathtouch: A creature with both First Strike/Double Strike and Deathtouch can destroy blocking/blocked creatures before they deal damage
Lifelink: A creature with both Double Strike and Lifelink will cause its controller to gain life twice
Trample: A creature with both First Strike/Double Strike and Trample can deal excess damage to players in both damage steps

Example Combat Scenarios

First Strike vs. Non-First Strike

When a 2/2 creature with First Strike blocks or is blocked by a 2/2 creature without First Strike:

First Strike creature deals 2 damage in the first strike damage step
The other creature is destroyed before it can deal damage in the regular damage step

Double Strike vs. Regular Creature

When a 2/2 creature with Double Strike blocks or is blocked by a 3/3 creature without First Strike:

Double Strike creature deals 2 damage in the first strike damage step
The 3/3 creature survives with 1 toughness remaining
Both creatures deal damage in the regular damage step (2 more from Double Strike, 3 from the regular creature)
Both creatures are destroyed

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