Wyverns are a D&D classic, but I’ve grown bored with their niche. They are cool draconic monsters with a twist (their sting), but often get relegated to the role of mount or pet. Here I redesign the wyvern to highlight its sting and make it feel more like a real-world poisonous monster.

Generally poisonous creatures are small, and a little weak. Because they have powerful venom they do not need great physical strength. Scorpions and vipers are terrifying in part because they are so small. It accentuates their unique abillity and allows them to get places larger creatures (say, a wolf) couldn’t. Throw these at a low level party and they will have a memorable encounter. Because they tend to attack horses etc. first, this should give the players a fighting chance while showcasing the monster. (I have a hard time eyeballing the CR of my new, sleeker wyvern, so use it with care. Players can get angry if you hit them with crippling ability damage and they have no way to mitigate it.)

Note: Constitution damage will kill a character reduced to 0 Con, and hit point damage will kill a character reduced to -10 hp, but the combination won’t (at least, not always). Every time a character loses 2 points of Con they lose 1 hit point per level, but no matter how much health they have remaining they will not fall under 1 hp by Con damage until their Con score reaches 0 (when they die).

Wyvern, Small BeastHP: 25 (4 HD)
AC: 18 touch 14 flatfooted 15 (+4 natural, +1 size, +3 Dex)
Initiative: +3
Saves: +4/+3/+3
Attack: +4/Grapple+4
Full Attack: Sting +4 damage 1d4+1 plus poison, Bite +2 damage 1d4+1
Special Abilities: Low-light vision, Scent
Skills: Hide +15, Listen +11, Move Silently +11, Spot +16
Poison: Fort DC 17, initial damage 2d6 Con, secondary damage 2d6 Con
At night you see a few shapes moving in the darkness among the branches. It looks like large animals are moving quickly through the treetops, quickly and silently. Once you catch a quick glance of a leathery wing silhouetted against the ever present moon.
Wyverns are solely nocturnal, and hunt at night with a combination of low-light vision and scent. They are attracted to large animals and will often attack a traveler’s horse or mule at night first, landing silently and injecting deadly venom. They can be repelled by burning dried woodsage on your campfire; they cannot abide the smell as it harms their Scent ability.
Wyverns attack!
Two creatures glide out of the gloom and land on the mules. They are greenish, reptilian beasts with a wingspan of six feet. They fold their leathery wings and hold on with claws as they sting with bony, segmented tails like those of scorpions.
Suddenly a heavy weight slams into your back, knocking you forward off balance. A large winged creature the size of an eagle is clinging to you, sharp claws digging into your back. It may weight about 30 lbs. It’s difficult to see as wings are beating around your head.