This increasingly large family of weapons is notable for scoring bonus damage on units of a particular class. There are four classes of unit in Fire Emblem Heroes: Infantry, flier, cavalry and armor. These weapons deal an extra 50% damage to units of one of the aforementioned classes. For instance, all bows deal bonus damage to fliers, but the Poison Dagger is the only weapon that deals bonus damage to infantry. The effects of these weapons come at the cost of lower might, but can be useful especially if your team has a weakness to a unit type.
These weapons have very limited synergy, being largely self-sustaining in their nature. They need no other skills to operate at maximum efficiency. However, as they multiply damage by 1.5x, buffs that boost attack stack very well with them. Hone Atk and in particular, class buffs that boost attack will provide sizeable increases to the damage. Specials such as Glimmer that increase damage also work decently well with these weapons.
Despite their advantages, these weapons are rarely used for their effects alone. Wolf tomes for instance, are rarely seen in comparison to Bows, who pack the effect as a bonus in addition to other effects and higher power. There are two large problems stopping these weapons from being effective. Firstly, they are useless when facing no enemies of the opposing class (anti-infantry weapons are slightly exempt from this, as infantry is very common). Weapons such as Raven tomes have a very high chance of being useful, in comparison. Secondly, they offer no defensive benefits against the units in question. While skills such as Triangle Adept offer both offensive and defensive benefits, type effective weapons are purely offensive, which makes them less viable on defensive units.