Mimics

A mimic is a shape-shifting predator which takes on a seemingly harmless or even enticing form in order to lure its prey to it. In the Ultima series, mimics consistently take on the shape of treasure chests. They appear in Ultima I, IV, V, VI and Ultima IX and are found universally in dungeons.

Description
While mimics are supposedly capable of taking on a variety of forms, the Britannian mimic seems to have a marked preference for appearing as a chest. Appearing harmless until approached, a mimic will assault unprepared treasure-seekers with a jet of venomous spittle before preceding to bite and claw at their prey in an attempt to consume it in its weakened state. In a later incarnation during the time of Ultima IX, not content to always sit in wait, mimics showed a capability to sprout limbs and chase down their victims on foot.

Trivia

 * Mimics are very likely derived from an eponymous creature in the table-top role playing game,  Dungeons & Dragons. The mimic first appeared in the Monster Manual published for the game in 1977, where it is described as having similar powers of disguise as the creatures featured in Ultima. In addition to these, it is also able to release adhesives to entrap its prey, which it then attacks with pseudopods.