The Mongols have four unique Ranged Cavalry units: the Nomad (II), Steppe Nomad (III), Horde (IV), and Golden Horde (V). Their listed benefit is that “they’re particularly effective against enemy Light Infantry” and “effective against enemy Musket Infantry”. The game confers these advantages by giving all four units a +60% damage bonus against Light Infantry and a +45% damage bonus against Gunpowder Infantry.
In reality this ends up being a really weird bonus to have. Not only do they still normally lose in fights against those units, but those same units are supposed to be counters to Ranged Cavalry, making these bonuses unintuitive for both the attacker and the defender.