Patrick Roy to the Avalanche (1995)

The Montreal Canadiens' decision to trade Patrick Roy to Colorado in December 1995 remains a franchise-defining blunder. After Roy publicly humiliated his coach and management following a 11-1 loss to Detroit, Montreal dealt him to the Avalanche for a package centered on Jocelyn Thibault. Roy immediately transformed Colorado, posting a 1.89 goals-against average and .923 save percentage in the 1995-96 playoffs, leading the team to a Stanley Cup victory in his first season. The trade shattered Montreal's reputation and cost them a Hall of Fame goalie who would win two more Vezina trophies with Colorado. Compared to #9 on this list, this trade's impact was 40% more immediate, as Roy's playoff heroics occurred just five months after the deal, whereas Chris Webber's acquisition took years to yield results for the Kings.