Any scarfed pokemon with a higher speed stat, such as flygon or jirachi could cause problems with that electivire, although you do at least have 3 ground resists which works nicely. CB scizor, who isn't weak to any of his attacks can OHKO with superpower, possibly OHKO with U-turn (89.7% - 105.8%) and 2hko with any other move. So I suggest you at least replace one of his moves with fire punch to avoid this, or go for a mixed attacker with flamethrower.
He also isn't a great DD gyarados check due to the fact that no DD gyarados would switch in on him, and if you switch in on the dragon dance then he outspeeds you and will most likely OHKO you first unless it's a bulky variant, in which case waterfall will only do 87.3% - 102.7% so there's still a chance he will if he doesn't switch.
I think if you maybe put a choice scarf on your starmie, or on your gengar (replacing a move with thunderbolt) then you would have a lot less to fear from gyarados.
Other than that, nice team!