mimicry
In evolutionary biology, mimicry is an evolved resemblance between an organism and another object, often an organism of another species.
As a tag, mimicry covers creatures that resemble something, but on closer inspection or after they reveal themselves are something completely different. This is can be acomlished with the ability to shapeshift, body shapes and colors that resemble something else, a disguise, or many other tricks.
Notable real world examples include flower mantises and phasmids.