Thanks for bringing up Pavano. He was 9-8 in 2009 with the Indians but with an ERA over 5 when the Twins dealt Yohan Pino for him. Pavano replaced an injured Glen Perkins in the Twins rotation, going 5-4 and also starting game 3 in the ALDS. (Perkins was demoted to AAA instead of being sent on a rehab assignment - which Perkins claimed was done to keep him from qualifying as a Super 2 for arbitration.) Pavano's real impact came the next season when he won 17 games for Minnesota and pitched 7 complete games. The rest of the staff was solid, too, as Blackburn, Baker, Slowey, and Liriano all made 28 or more starts and all won 10 or more games. (Duensing also won 10 in mixed duty)
Actually, Pavano pitched well after the trade, but his W-L didn't reflect that, which shows just how hard it is for one non-superstar to make a big impact in a mid-season trade.