Also consider Will o' Wisp. It lets Rotom be an amazing crippler. You can ruin walls like Blissey with the scarf, the ruin a physical sweeper with Will o' Wisp, and then still be able to hit with good STAB moves in Thunderbolt/Volt Switch and Hydro Pump. If you are better at predictions then your opponent, it's a very good Pokemon.
Why would you run Will-o-wisp on a Choice Scarf set?~de