the Sniper is a cut zombie type from Zombie Master.
The Sniper were to be a small zombie that spits acid saliva on the survivors, nothing else is known about him, just because he has a small health.
He was probably cut because he was a bit annoying, because he can spits from an absurd distance and destroy barricades without getting close to the survivors.
As seen in the files, the Sniper were to use the same saliva projectile from the Antlion Worker from HL2
The Sniper is very similiar to the Spitter from Left 4 Dead 2, because they both spits acid saliva and have a low health.
As seen in the files, the Sniper were a kind of green Drifter model, and players who get closer to him will be burned by his acid.
The Sniper seemed to glow in the dark as seen in the picture