One who shifts or reassigns the blame or responsibility (for something) to another person, group, or thing. Every politician becomes a buckpasser when they fail to deliver on their promises. Maybe instead of being a buckpasser, you should have a think about what you could be doing to improve your performance.

slang Someone who administers anesthesia (which comes in gaseous forms). Once the gas-passer is done, we'll go ahead in and start operating.