Giant Venomous Snake

A giant venomous snake on the party's side is a druid wild shape, a warlock familiar, or a marsh witch's gift. Name the framing outright so the table understands why this CR 1/4 snake is an asset.

Use it for a single job and withdraw. The 40-foot swim makes it a courier across flooded terrain. Blindsight 10 feet lets it navigate pitch-black caves or flooded cellars. In combat, the snake is a glass cannon. 11 HP means one hit kills it. Send it up a wall to drop on a flanking enemy, strike once, then pull it away before the counterattack lands. Dex 18 means it has first-round initiative. Spend that on positioning, not on melee.

If it's a druid's wild shape, the player controls it. If it's on loan from a witch, treat it as temporary. When the favor is repaid or the day ends, the snake leaves through the nearest water without goodbye. Snakes don't bond like dogs.

Let the snake live through the session. A table that names a creature with 11 HP cares more about the next swamp encounter for it.

A giant venomous snake is a CR 1/4 ambush predator with 11 HP, AC 14, Dex 18, a 10-foot Blindsight, and a Bite at +6 for 1d4+4 piercing plus 1d8 poison. It moves 40 feet walk and 40 feet swim. It kills in one good hit if it gets the jump, and dies in almost any hit if it doesn't.

Stage the surprise before combat. Blindsight 10 feet is short range, so the snake should be coiled in a reed bed, under the wagon, or in tall grass when the party arrives. The snake's Initiative 14 and Dex 18 mean it strikes first if the party doesn't see it. Roll the Bite attack behind the screen. Call out the hit or miss before naming the attacker. The party learns there's a snake from your narration, not from your monster list.

The snake has 11 HP. One good hit kills it. If you want more than one round of encounter, run two or three snakes in different positions. Spread them across the terrain: one in the water, one in cattails, one on a low branch. The 40-foot swim speed lets a wounded snake dive into the river, circle underwater, and strike from a different angle.

Below half HP, the snake flees. Beasts don't die for pride. Let it slither into the water or underbrush. The party should remember the snake as the thing that forced a poison save, not as a 50 XP kill.