In the Sa2 saga, he and Sonic fought evenly. Then he sacrificed himself in the end, which took out the Biolizard, that's one win for him. Then in Season 3 when he's returned, he take out some minor enemies (Matarex bots). In the episode titled "The Cosmo Conspiracy" he takes out Sonic, Chris, and Knuckles. Then in the end of the show, thanks to Cosmo's help, both he and Sonic was able to defeat Dark Oak, the final villain of the show. So Shadow literally won every fight he have been a part of either by himself or with some help. The only legit fight he would lose in is that at one point in episode 38. Shadow made a statement that he can't get passed through the G.U.N soldiers to save Maria in the past. But that was the past, surely his powers could have evolved. And, we never exactly see Shadow losing to GU.N on screen.