Large Beast
Armor Class 13
Hit Points 45 (6d10+12)
Speed swim +40, walk +20
Challenge 7
Senses passive Perception 11
Hold Breath. The plesiosaurus can hold its breath for 1 hour.
Bite. Melee Weapon Attack: +6 to hit, reach 10 ft., one target. Hit: 15 (2d10 + 4) piercing damage. The target makes a DC 14 Strength saving throw. On a failure it is pulled up to 5 feet towards the plesiosaurus.
Source: Level Up Advanced 5e Monstrous Menagerie · OGL/Open