n medium animal 

Perception +7; low-light vision

Skills Acrobatics +9, Athletics +8, Stealth +8, Survival +6

Str +3 Dex +4 Con +3 Int -4 Wis +1 Cha -2

AC  19; Fort +8, Ref +11, Will +6

HP 26

Coiled Opportunity [R] If the giant viper is coiled and a creature moves into or through a square adjacent to it, the giant viper can use its reaction to make a fangs Strike against that creature.

Speed 20 feet, climb 20 feet, swim 20 feet

Melee [>] fangs +11 (finesse), Damage 1d8 + 3 piercing plus giant viper venom

Coil [>] The giant viper uses an action to coil itself. While coiled, it can target a creature up to 10 feet away with its fangs Strike. After the giant viper Strikes with its fangs, it becomes uncoiled.

Giant Viper Venom (poison) A target damaged by the snake's fangs must succeed at a DC 17 Fortitude save or take 1d12 poison damage.

Beginner Box, page 77.