You should EV train your Gible in Attack or Special Attack depending on what kind of moveset you're using (I'd recommend a Physical set, so Attack EV's would be best), and the remaining EV's can go into Speed if you want to outspeed things, or HP if you want your Gible to take lots of hits. If you'd like a moveset too, just ask and I'll edit this answer with one. :)
-Crunch/Brick Break/Rock Slide/Aerial Ace
Dragon Claw is your dragon-type STAB, and Earthquake/Dig is your Ground STAB. Dig is an option if you can't get the TM for Earthquake. Swords Dance is to set up and become even more powerful, and the last slot is a coverage move of your choice. Rock Slide or Brick Break would be the best for covering Ice types....I don't know why you'd stay in on an Ice type, though.
And for your item...I haven't played Platinum before, so I don't know how hard any of them are to obtain in-game, so I'll just list a few that should be useable. Kings Rock, Draco/Earth Plate, Expert Belt, Shell Bell, or Scope Lens.
Hope I helped!