Animorphs: Transformers was the first of several spin-off crossover series pioneered by Hasbro. Animorphs, like the others, bears no in-fiction ties to the rest of the Transformers universe, but used the Transformers brand name to promote their shape-changing action figures. The line was very short lived, spanning only a portion of 1999.
The Animorphs toyline was based on a book series describing humans that could fluidly morph into animals. However, the toys had to approach the problem from the typical angle of rearranging body parts to produce both forms. This generally left the humans not-fully-human, favoring a more homogenous beast form. The humans were generally dressed in tattered clothes, painted in colors that contrasted the character's alternate form. Given the aesthetic difficulties in producing a recognizable “human” from a beast, accessories were often used to complement the morph, covering human hands or other parts.
Each deluxe-class figure also included an evil “Yeerk”, a slug-like creature not to scale with the figure. Each Yeerk was packed in a random color: red, orange, or purple. Most figures also included a “hybrid” head for the human form, showing the human's face mid-way to the alternate form. A final subseries was designed that depicted animal-to-animal morphs, but was scrapped when Animoprhs was cancelled. They were later ported to Beast Wars as the Mutants. The line's cancellation also resulted in two figures not being released outside of Europe, and thus becoming quite rare.