A Trammeler is a monster that's mentioned in Might and Magic: The Dreamwright, and appears in Might and Magic: The Shadowsmith. It lived in the Aulmad and the Siccative, and spun illusions to trick travelers into their dens.
When Diligence's caravan was traveling to Paddifraw's Repose, Dopple and Brevny reported that they had seen a great battle in a basin ahead. Shevoss and Varve rode out to investigate, but saw no traces of combat. Welleck suggested that a trammeler was at work, or some other force capable of creating illusions. It later transpired that Pomponderant was watching an illusionary recording of the Rout of Red Harra.
Jassad Attqua and Hitch were later traveling through the Siccative on their way to the golden ship, with Jassad carrying Hitch on his back as he ran. Suddenly, Hitch spotted a group of noose women straight ahead and shouted at him to avoid them, but Jassad saw nothing. They soon learned that a trammeler was casting illusions at them, trying to herd them into its lair, but The Reference allowed Jassad to sort the false images from the real ones. While Hitch saw plenty of disturbing images after this, he soon learned to trust Jassad's eyes.
When they entered the Blasted Lands, they met up with Varve, who was traveling in the broken shell of one of the caravan's wagons. He told them he'd managed to get past the trammelers by using plugs of dried river-squash as ear-plugs, and a broad black sunbonnet he'd found to shield his eyes. This allowed him to just travel on, ignoring whatever they sent at him.