The Poison Spear is a craftable Weapon exclusive to the Shipwrecked DLC. It does the same damage as a Spear and Poisons the target on hit.
Poisoned enemies move slower, attack less often, and deal less damage. However, the fooditems that drop from poisoned enemies will have their freshness reduced to 50%.
Tips
The Poison Spear is a useful melee weapon in killing Prime Apes as it slows their movement speed on each hit.
Because of its ability to slow down and weaken enemies, this weapon is excellent against Bosses like the Tiger Shark; or in Reign of Giants linked worlds, against the Dragonfly due to her fast attack period, making it safer to land a hit and kite while she's poisoned.
Loaded into a Spear Gun, the Poison Spear makes a great first strike against a Blue Whale/White Whale. The spoilage penalty on loot will not apply and the whale will move and attack much slower.
Prior to the Hang Ten update, the Poison Spear's icon looked just like a regular Spear with its tip being green.
Like in every other case, crafting does not consider durability of an item, making a 1% Spear just as good as a 100% one, effectively letting the player use a spear almost twice as long.