At the very least, try those out. Mamoswine has decent speed, and Avalance has that negative priority. This also leaves you a bit weak to the rare lead Gyarados. Endeavor, Protect, or Stone Edge help out with that.
Wish is excellent especially since you don't have a Rapid Spinner. Heal Bell/Aroma Therapy might not be as nearly useful as you might think, so you might want to test out an elemental attack of your choice. Thunder Wave, as long as you can avoid hitting Electivire, is I think much more useful than Toxic, and has better accuracy.
Scizor and Dragonite are fine.
HP Dark is a horrible Hidden Power because nothing takes x4 damage from it. Think of Hidden Power like this:
Hidden Power has the max base power of 70. For super effective damage (x2), it hits for 140 damage. For quad damage, it hits for 280.
Compare that to STAB Surf, which hits 120 for neutral damage.
This means you only want to use Hidden Power for x4 damage. That is HP Ice, HP Fire, HP Fighting, HP Electric, HP Ground, and HP Grass. HP Ice is by far the most common, the others less so.
Starmie doesn't need HP Ice, Grass, or Electric due to Ice Beam, Grass Knot, and Thunderbolt. The major baddie who takes x4 from Fighting also take x2 damage from STAB Surf. That leaves HP Fire, which'll hit Scizor.
You can put HP Fire on Choiced Starmie or Grass Knot, depending on if you want to hit Scizor or Swampert. Trick is also an option and will cripple special walls such as Blissey and Snorlax.