Ash Sting Wyvern (young)

Ash Scales. The Ash Sting wyvern features a dark soot stained scale complexion. Often large scales that can easy be mistaken for Rocks. As such in mountainous or rocky environments it has Advantage on Stealth (dexterity) checks.

Mutated. The Ash Sting is a cousin to the Wyvern. Born near volcano's or other ash covered lands, these creatures evolved to suit the environment. But furthermore, volcanos being extreme deposits of elemental fire magic has tapped into the draconic creatures natural disposition for magic (dragons were and are highly magical creatures so some may be more disposed to magical effects than a normal beast). As such they are far more intelligent then the average Wyvern. Use traps and enviromental effects, and flee when mortal, don't be afraid to play tricksey when running this Wyvern.  

Fire through the veins. This Wyvern has a weaker sting however it has a more lasting effect. The poison continues to burn through the body as it spreads. Dealing 2d4 points of fire damage. This damage stops after a DC 12 medicine check as an action or any points of healing. The poisoned effect does not go until a Dc 14 con save is succeeded at the end of every turn.

Multiattack. The wyvern makes two attacks: one with its bite and one with its stinger. While flying, it can use its claws in place of one other attack.

Bite. Melee Weapon Attack: +5 to hit, reach 10 ft., one creature. Hit: 6 (1d6 + 3) piercing damage.

Claws. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 7 (1d8 + 3) slashing damage.

Stinger. Melee Weapon Attack: +5 to hit, reach 10 ft., one creature. Hit: 6 (1d6 + 3) piercing damage. The target must make a DC 14 Constitution saving throw, taking 12 (4d6) poison damage on a failed save, or half as much damage on a successful one.

Fleeing in danger. When the Wyvern feels the need to flee as a reaction after taking damage it can breath a cloud of ash out. This acts as a fog cloud for purposes of range, width and the effects. However it disperses at the end of the Wyverns next turn.