During the battle on the Firehouse roof, one shot shows two Rays and no Winston.
During the fight at the abandoned warehouse, when Slimer is scared by the ghost, his tail rapidly switches color from his regular green to the same shade of brown as the rain clothing Slimer wears. In all other shots, the clothes are yellow instead of brown.
When Peter says "I got 'em" during the fight at the abandoned warehouse, the same shot that Ray saw earlier on their haunted TV is seen again, including the frame of the television screen all around it.