Plesiosaurus

Large beast, unaligned
Armor Class 13 (natural armor)
Hit Points 68 (8d10 + 24)
Speed 20 ft., swim 40 ft.
STR
18 (+4)
DEX
15 (+2)
CON
16 (+3)
INT
2 (-4)
WIS
12 (+1)
CHA
5 (-3)
Skills Perception +3, Stealth +4
Senses passive Perception 13
Languages -
Challenge 2 (450 XP)

Hold Breath. The plesiosaurus can hold its breath for 1 hour.

ACTIONS

Bite. Melee Weapon Attack: +6 to hit, reach 10 ft., one target. Hit: 14 (3d6 + 4) piercing damage.

This predatory marine reptile and cousin to the dinosaurs attacks any creature it encounters. Its long, flexible neck lets it twist in any direction to deliver a powerful bite.
Monster Manual (SRD) D&D 5 › Monsters