Plagarrat is based on a Black Rat, its appearance is similar to its pre-evolution with relatively short limbs and a predominantly black body with splotches of green around the neck and rear, in addition the evolution has darker splotches of green that extend further than the brighter splotches, it also has darker splotches around the base of each of its limbs. The Pokémon has a longer body making its grey underbelly more prevalent in the design, in addition the underbelly has white stripes that are separated by a small stripe of black fur from the grey fur. Its legs are slightly longer allowing the Pokémon to more easily keep its body off the ground although leaves it sill quite short vertically overall, its limbs have slightly more developed digits with longer claws allowing it to more easily grip onto things. the pipe-like design of its tail remains although it appears to have built onto the design with silver nuts connecting segments of its tail together, when its attacked it can lose a bit of its tail from attackers, when it grows back a nut appears at the base of the new segment.
The Pokémon's head has a rather distinct design, while appearing mostly unchanged from its pre-evolution, the Pokémon now has two taps where its ears would be located, when the Pokémon is sent into battle it will unscrew these taps revealing its ears underneath. Its eyes and mouth appear unchanged, its nose is slightly more prevalent appearing to stick up from the rest of its head. The single tuft of fur from its pre-evolution has developed into a cowlick which hangs down to just in front of Plagarrat's eyes before curling back up.