これを考えると:
string msg = string.Format("Duckbill {0} Platypus has not been loaded. Fetch Duckbill {1}'s Platypus then continue.", userDuckbill, userDuckbill);
...代わりにこれを行うだけで十分でしょうか:
string msg = string.Format("Duckbill {0} Platypus has not been loaded. Fetch Duckbill {1}'s Platypus then continue.", userDuckbill);
?