Monster Manual, page 80
Plesiosaurus CR: 2
Large beast, unaligned
Armor Class: 13 (natural armor)
Hit Points: 68 (8d10+24)
Speed:
20 ft
, swim: 40 ft
Skills: Proficiency Bonus +2, Perception +3, Stealth +4
Senses: Passive Perception 13
Languages: - -
Challenge Rating: 2
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.
Suggested Environments
Coastal, Underwater