Nature should be Modest, Fire-blast should be replaced for the more reliable Flamethrower, and U-turn should be replaced for Surf. Also 252 gives as many stat points as 255 so give him 252 S.Attack, 252 Speed, and 4 Hp for an extra HP stat so as not to waste any stat points.
Give him 4 Evs in Hp. Give him Leftovers as the Item, Nature should be Timid, moves should be Thunderbolt, Nasty-plot, HP(Ice), and Dark-pulse. Or you could go annoy+Switch same Item, EVs, Nature, though the moves should be: Thunder-wave, Volt-switch, HP(Ice), and Grass-knot.
Make his Ability: Sniper, then Swap Crunch for Night-slash. You may consider Swapping Ice-fang for Whirlwind so as to cause more Pokemon to take damage from entry hazards though you would have to wait for Ferrothorn to set up too.
Good, you could consider swapping X-scissor for Swords-dance, but that is only if you switch Choice-band for the Muscle band which is a very good idea because it allows more freedom of moves.
Explosion is waaaaaay worse in this Gen swap for Gyro-ball. Also swap Toxic for Curse to boost stats. Give him Brave nature so he can actually have a beneficial nature. EVs should be: 252 S.Defense, 158 Hp, 100 Defense.
Dragon-claw is better than Dragon-rush. Earthquake is WAY better than Iron-tail.