Unliked pokemon ... hmm lets give it a try.
Still a speed sketch but did find a very similar critter in real life to base Patrat on.
Dinagat Bushy-tailed Cloud Rat ( Crateromys australis )

Treeclimbing rat type and only missed the darker stripe around it's eye as the design in the pokemon but otherwise very similar. Did a bit color variants as well ... werent so sure about the albino looking one, so made one lighter. Didnt feel like to draw a completly white and with red eyes.
Just examples and could be lighter, darker or even more striped/spotted to hide better in the foliage of the trees and branches.