Quipper

Tiny beast, unaligned
Armor Class 13
Hit Points 1 (1d4 - 1)
Speed 0 ft., swim 40 ft.
STR
2 (-4)
DEX
16 (+3)
CON
9 (-1)
INT
1 (-5)
WIS
7 (-2)
CHA
2 (-4)
Senses darkvision 60 ft., passive Perception 8
Languages
Challenge 0 (10 XP)

Blood Frenzy. The quipper has advantage on melee attack rolls against any creature that doesn't have all its hit points.

Water Breathing. The quipper can breathe only underwater.

Actions

Bite. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 1 piercing damage.

A quipper is a carnivorous fish with sharp teeth.
Monster Manual (SRD)
Quipper