Trelon

Survivors describe a trelon as orange light tangled up with shadow. It stands on two stilt-thin legs, carries two long arms ending in hooked spikes, and has a pair of feeding mandibles beside the mouth. The talons grow long enough to serve as sword blades.

A swarm is simply not there until prey comes within 30 feet. Then the trelons take shape out of the gloom at once, imposing a -3 penalty to surprise. They only appear in shadowy spots with no natural light, and where they come from or retreat to is unknown. The swarm mobs everything in reach, closing its paired armspikes like shears, and feeds only after every non-trelon is dead.

Nobody knows how they track prey, though magical concealment never fools them. Invisibility, dust of disappearance, displacement and shadow magic draw them in, and any cloaked target in range enrages the swarm into attacking it first. Torches or strong lanterns can keep a trelon off its quarry, but light spells drive them to frenzy against the caster. Hold monster, protection from evil, mind-influencing spells, illusions and shadow magic all fail against them.

Legend holds they were bred on a dead world to exterminate its mages, and they certainly hate wizards and magic. A sorcerer of the neutral planes once loosed a swarm inside an academy of illusionists near a gate-town, and every student died asleep. Trelons click and chitter, rising to a deafening shriek in battle. Some sages suspect a hive mind, but that is guesswork.

Part fiend, part insect, trelons favor cool, dim places and swarm at the scent of a wizard or of magic. Their claws are components for weapons that slay illusionists, shadows or ethereal beings, and an enchanted talon makes a mage-killing blade said to twist toward any magic-user nearby. Rumor says the swarm returns for such stolen pieces. Trelon blood reportedly lends unknown powers to arrows of slaying against mages, illusionists and shadows, but using it to strengthen a spell or ritual makes the magic fail and sometimes summons a swarm.