Here's my version of a realistic Serperior evolution line. The original concept was inspired by Arvalis. He has made many amazing realistic Pokemon. Check him out! [link]
The Serperior evolution line is unique because the youngest member, Snivy, has lizard-like legs which it uses to chase down prey such as Ledyba and other Bug Pokemon. However, once evolving into Servine, the body becomes much stockier and the legs and arms become smaller. Then once Servine evolves into Serperior, the legs completely disappear and the arms are reduced to tiny spines. The loss of the use of arms and legs have made Servine and Serperior into ambush predators, unlike Snivy.
All three Pokemon have strange leaf-like collars around their necks, which are actually sections of loose skin that act as camouflage in jungles and forests. Snivy and Servine have small, leaf-like fins on the tips of their tails which also act as camouflage. Servine even has two of these fins on their back. All three also have modified scales on their tails that resemble the thorns of a plant. These are usually used for self-defense.
While the average length of a Serperior is 10' 10'', some individuals have been reprted to grow as long as 18 feet. These larger specimens have been witnessed going after prey items as large as Sawsbuck.