Algoid

At first glance an algoid passes for a crude green-skinned humanoid, sometimes taken for a troll. It is actually a colony of intelligent algae cells clumped together to move. Depending on how many cells join in, it stands 5 to 7 feet and weighs 115 to 250 pounds.

It hammers downward with two big fists for 1-10 each. On a natural 19 or 20 the blow deals the full 10 and stuns the target for 1-4 rounds.

Cutting and piercing weapons below +2 do nothing to it, and those of +2 or better do half damage, while blunt weapons deal full damage even without magic. Fire and electricity, magical or otherwise, cannot harm it. Three water spells hurt it badly: destroy water, lower water and part water each inflict 1-6 per caster level, to a maximum of 10d6; other spells work as usual.

Through an empathic bond with cypress, willow, water-oak and similar water-loving trees, it can animate one or two to fight. These trees move at 3 and strike twice a round for 1-10, with a THAC0 based on size but never worse than 15.

Algoids need water nearby, fresh or salt, still or moving, though slow rivers and streams are favored, and river deltas host some of the strongest colonies. They share a hive mind with no ranks. The colony only forms bodies when threatened or relocating, joining nearby cells into walkers, and the groupings change, so a cell might be in a 250-pound body today and a 170-pound one tomorrow.

As plants they live by photosynthesis and breed best in warm brackish water, though cold water works too. Deprived of daylight for longer than a few days, they die, darkening steadily until nearly black. This is a starvation death, and a good-aligned character should never inflict it. Priests and alchemists prize the black remains, powdered into salves and used in refining gold ore. Algoids killed in battle and left in the dark just rot like any vegetation.

This rare arctic variety lives off snow, ice and thin sunlight. It cannot command trees but talks with small sea crustaceans, which lure fishing boats close. The algoid swims beneath and punches holes in the hull, then eats the wood while the crustaceans feed on the crew. Starved of light it turns a glowing blue rather than black, and the powder makes a cloth dye.