Complex sentence: During the costume contest, one of the mayor's sons, Matt, picks a fight with Trantor by a big mistake, into thinking it was Kenny, Trantors attacks Matt, resulting in Matt turning the boy into his fifth and final wooden doll.
Split into simpler sentences: During the costume contest, one of the mayor's sons, Matt, picks a fight with Trantor by mistake, thinking it was Kenny. Trantor attacks Matt, resulting in Matt turning the boy into his fifth and final wooden doll.