Merfolk (CR 1/2)

Medium Humanoid (Aquatic)
Alignment: Usually neutral
Initiative: +1 (Dex); Senses: low-light vision, Listen +3, and Spot +3

AC: 13 (+1 Dex, +2 leather), touch 11, flat-footed 12
Hit Dice: 1d8+2 (6 hp)
Fort +4, Ref +1, Will +1
Speed: 5 ft., swim 50 ft.
Space: 5 ft./5 ft.
Base Attack +1; Grapple +2
Attack: Trident +2 melee; or heavy crossbow +2 ranged
Full Attack: Trident +2 melee; or heavy crossbow +2 ranged
Damage: Trident 1d8+1; or heavy crossbow 1d10/19-20
Special Attacks/Actions: -
Abilities: Str 13, Dex 13, Con 14, Int 10, Wis 9, Cha 10
Special Qualities: Amphibious
Feats: Alertness
Skills: Listen +3, Spot +3, and Swim +9
Advancement: By character class
Climate/Terrain: Temperate aquatic
Organization: Company (2-4), patrol (11-20 plus 2 3rd-level lieutenants and 1 leader of 3rd-6th level), or band (30-60 1 3rd-level sergeant per 20 adults, 5 5th-level lieutenants, 3 7th-level captains, and 10 porpoises)
Treasure/Possessions: Standard

Source: Monster Manual

Merfolk favor heavy crossbows of shell and coral that fire bolts fashioned from blowfish spines, with an underwater range of 30 yards. Merfolk often barrage their enemies before closing, when they resort to tridents.

Aquatic Subtype

Creatures with the aquatic subtype always have swim speeds and thus can move in water without making Swim checks. An aquatic creature can breathe underwater. It cannot also breathe air unless it has the amphibious special quality.