reliever

someone who takes the place of another (as when things get dangerous or difficult); "the star had a stand-in for dangerous scenes"; "we need extra employees for summer fill-ins"

Source: WordNet® 3.1, Princeton University — "WordNet Copyright 2011 by Princeton University. All rights reserved." Used under WordNet's license terms. See methodology for full licensing detail. Word validity for game play may differ from any official game dictionary.