The Sabres also acquired a pair of second-round draft picks in a deal made just before the NHL's trade deadline hit Wednesday.
Moulson changes teams for a second time this year after the Sabres acquired him in a deal that sent leading scorer Thomas Vanek to the New York Islanders in October. In his seventh NHL season, Moulson is a three-time 30-goal-scorer, who has 17 goals and 38 points in 55 games this season.
McCormick was a fourth-line role player during his four seasons in Buffalo. He has split this season between Buffalo and AHL Rochester, and has one goal and five points in 29 games with the Sabres.
Mitchell is in his sixth NHL season, and second with the Wild after spending his first four years with San Jose.
Mitchell had difficulty playing a significant role in Minnesota, where he had a goal and nine points in 58 games this season.