Victini Lv. 48
you'll want a water pokemon here because it resists Victini's fire attacks. Ground pokemon dont, which makes them take more damage from victini's attacks. a Flash fire pokemon like lampent would really help too.
Serperior Lv. 57
Pretty much any fire type. It doesnt have perversity, so you dont have to worry about leaf storm.
Klingklang Lv. 49
Klinklang only has access to Normal and steel attacks, as well as some weak electric ones. Any steel type can really slam it. Excadrill is probably the best answer in the game you have for his klinklang. you can find one near the end of victory road (look for the dirt spots).
Swanna Lv. 48
Pretty much any electric attack will KO this thing. this shouldnt be too much of a problem.
Zekrom lv.52
Biggest problem. your best bet here is to use that excadrill, or use some other type of really strong ground pokemon. Ground types are immune to the STAB Electric attacks zekrom has. you could also use Will o wisp to burn it so that Lightning strike and crunch will only do half damage.
Stoutland Lv. 48
Fighting attacks for super-effective damage. i'm not sure what attacks Stoutland has, but any steel type can resist its Normal attacks.
in general, get an excadrill, a solid Fighting type, and a good STAB electric attack. it would really help out if we knew the attacks the pokemon knew, too.