Weapon effectiveness

Weapon effectiveness is a damage modifier associated with certain weapons that grant them the ability to deal bonus damage against units or objects with certain attributes (e.g., armor, flight). The bonus damage formula is different for each game and in some English releases.

Description
In general, attacks with weapon effectiveness are treated as normal hits with increased might, so they can hit/miss, activate critical hits, or trigger skills like any regular attack. In Fire Emblem: Genealogy of the Holy War, however, weapon effectiveness guarantees critical hits. Weapons with weapon effectiveness otherwise deal normal damage against units who do not possess the attributes relevant to said weapons (except in Fire Emblem Fates).

Weapon effectiveness does not stack with skills, and it does not gain increased damage if the defending unit has more than one attribute that the attacking unit can exploit. As a general rule, games will always prioritize the damage modifier from weapons over any other possible factor that an attacking unit may have.
 * Consider this example from Fire Emblem Fates: an attacking unit has Golembane and is equipped with a Wyrmslayer. She has the ability to double her weapon might against Stoneborn, Puppets, and Mechanists from Golembane; and she also has the ability to triple the Wyrmslayer's weapon might when she attacks a dragon unit with it. The defending unit is a Mechanist Avatar. As a Mechanist, he incurs increased damage from Golembane holders. He also possesses the dragon attribute because of the Avatar's parentage, so he incurs increased damage from Wyrmslayer. When the attacking unit attacks the Avatar, the battle forecast will show an attack strength that factors in only the bonus from Wyrmslayer—this value will be treated as the base attack strength of the attacker for this battle.

Unless stated otherwise, bows deal effective damage against flying units.

Fire Emblem: Ankoku Ryū to Hikari no Tsurugi
In this game, weapon effectiveness triples the weapon's might.

Here is a table of weapons with the unit type against whom they deal effective damage:

Fire Emblem Gaiden
In this game, weapon effectiveness triples the weapon's might.

The Falcon Knight class possess an innate skill that allows them to deal effective damage against monsters.

Here is a table of weapons with the unit type against whom they deal effective damage:

Fire Emblem: Mystery of the Emblem
In this game, weapon effectiveness triples the weapon's might.

Here is a list of weapons that deal effective damage:

Fire Emblem: Genealogy of the Holy War
In this game, weapon effectiveness guarantees a critical hit (unless the defending unit possessed Nihil); essentially, this meant that weapon effectiveness doubled a weapon’s attack.

Here is a list of weapons that deal effective damage:

Fire Emblem: Thracia 776
In this game, weapon effectiveness doubles the weapon’s attack.

All wind magic tomes (barring Blizzard) deal effective damage against flying units.

Here is a list of weapons that deal effective damage:

Fire Emblem: Binding Blade
In this game, weapon effectiveness triples a weapon’s might.

Here is a list of weapons that deal effective damage:

Fire Emblem: Rekka no Ken
In the Japanese version of this game, weapon effectiveness triples a weapon’s might.

In the English releases of the game, weapon effectiveness doubles a weapon’s might.

Here is a list of weapons that deal effective damage:

Fire Emblem: The Sacred Stones
In this game, weapon effectiveness generally triples a weapon’s might.

Weapons indicated with an asterisk (*) double in might when they have weapon effectiveness.

The Bishop's Slayer skill allows them to deal effective damage against monsters. However, when a Bishop attacks with the Ivaldi tome, the game will prioritize Ivaldi's damage modifier over that of Slayer's.

Here is a list of weapons that deal effective damage:

Fire Emblem: Path of Radiance
In this game, weapon effectiveness doubles a weapon's might.

All fire magic tomes deal effective damage against Beast Laguz.

All thunder magic tomes deal effective damage against Dragon Laguz.

All wind magic tomes deal effective damage against flying units.

All weapons effective against Laguz only deal effective damage when Laguz are transformed.

Here is a list of weapons that deal effective damage:

Fire Emblem: Radiant Dawn
In this game, weapon effectiveness triples a weapon's might.

All axes deal effective damage against doors.

All bows, crossbows, ballistae, and wind magic spells (except for Wind Tail) deal effective damage against pegasi and Bird Laguz.

All fire magic spells (except for Fire Tail) deal effective damage against Beast Laguz.

All thunder magic spells (except for Thunder Tail) deal effective damage against Dragon Laguz and Dragon Knights. All weapons effective against Laguz only deal effective damage when Laguz are transformed.

The Beastfoe, Birdfoe, and Dragonfoe skills allow the users to deal effective damage against (respectively) Beast, Bird, and Dragon Laguz.

Here is a list of weapons that deal effective damage:

Fire Emblem: Shadow Dragon
In this game, weapon effectiveness triples a weapon's might.

Here is a list of weapons that deal effective damage:

Fire Emblem: Shin Monshō no Nazo ~Hikari to Kage no Eiyū~
In this game, weapon effectiveness triples a weapon's might.

Here is a list of weapons that deal effective damage:

Fire Emblem Awakening
In this game, weapon effectiveness triples weapon might.

The Beastbane skill allows the user to deal effective damage against units with the beast attribute when s/he is in the Taguel form.

The Wyrmsbane skill allows the user to deal effective damage against units with the dragon attribute when s/he is in the Dragon form.

The Conquest skill essentially negates the user's armor or beast weaknesses whenever applicable.

Units with the Taguel base class possess the beast attribute regardless of whatever class they occupy.

Units with the Manakete base class possess the dragon attribute regardless of whatever class they occupy.

All mounted classes (barring Wyvern Rider and Wyvern Lord) possess the beast attribute.

The Exalted Falchion and Parallel Falchion deal effective damage against the final boss.

Here is a list of weapons that deal effective damage:

Fire Emblem Fates
In this game, weapon effectiveness triples weapon might.

The Golembane skill doubles the user's weapon might whenever s/he is battling a Stoneborn, Puppet, or Mechanist. The effects of this skill do not stack with the effects of weapons with weapon effectiveness; in such cases, the game uses the bonuses from the weapon to calculate the user's damage output whenever applicable.

The Beastbane skill doubles the user's weapon might against units with the beast attribute when s/he is in a beast form.

The Avatar and any of his/her children possess the dragon attribute regardless of whatever class they occupy.

The Hunter's Bow deals effective damage against beast units but not flying units.

Whenever a unit uses a weapon with weapon effectiveness against another unit that does not have attributes relevant to said weapon, the user has his/her damage output reduced by 4 points and hit rate reduced by 10 points. The exceptions to this inhibition are bows/yumis, the anti-monster weapons and the Dragon Spirit.

Here is a list of weapons with weapon effectiveness: