The Thing From Another World. It's the name of the original 1950s movie that 'The Thing' is a remake of (which is in turn based on a 1930s novella "Who Goes There?"). It also happens to be the name that was used for the comic series that were based on 'The Thing' movie.
However, it's a perfect imitation, at the cellular level. By copying the Alien's exoskeleton, which is immune to the acid, it would become immune to the acid itself and then be able to copy the acid at its leisure.