Sources
CR
Type
Size
Alignment
Movement

Two-Headed Plesiosaurus

Large Beast, Unaligned

Armor Class 13 (natural armor)
Hit Points 100 (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 4 (1,100 XP)

Traits

Two Heads. The two-headed plesiosaurus has advantage on Wisdom (Perception) checks and on saving throws against being blinded, charmed, deafened, frightened, stunned, and knocked unconscious.

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

Actions

Multiattack. The two-headed plesiosaurus makes two bite attacks.

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

Lore

A two-headed plesiosaurus is a marine dinosaur whose compact body is driven by powerful flippers. Predatory and aggressive, it attacks any creature it encounters. Its flexible necks account for a third of its total length, letting it twist in any direction to deliver a powerful bite.