My changes/suggestions are in bold. I'll try to do items as best I can...
BLAZIKEN@Scope Lens/Shell Bell
-Bulk Up
-Sky Uppercut
-Slash
-Blaze Kick
This set goes for critical hits. High ratios and Scope Lens.
TROPIUS@Leftovers
-Razor Leaf
-Body Slam/Aerial Ace
-Leech Seed
-Synthesis
Sunnybeam is no longer a very good combo on grass types, even if they have Clorophyll. If you really wanted to do that set, definitely go with quake, you'll need it for fires. Otherwise, this set is good, and fun! You can do Bslam for paralysis, or Ace for STAB.
MILOTIC@Leftys
Fine, but do Mirror Coat if you want to breed over Confuse Ray. It works well, but the set you have is also fine.
METAGROSS@Leftys/Shell Bell
-Meteor Mash
-Shadow Ball
-Earthquake
-Agility/Light Screen
Focus more on attack, not both. And you need quake for fires. And Agility or LS to get rid of Iron Defense.
SALAMENCE@Leftys/Shell Bell
-Dragon Claw
-Crunch
-Flamethrower
-[b]Hydro Pump
Special set, lotsa fun. You could do physical, but I think special is better, especially if you use AAce on Tropius. (Requires breeding with Hydro Pump Gyarados; can take an incredibly long time, but worth it)
Drop Flygon; you already have 2 weak to ice (Tropius and Salamence), and both those are 2x weak to ice. And with flygon, you'd be technically 6x weak to ice, which is extremely common. For your last slot, consider an electric, maybe Manectric with Thunderbolt, Thunder wave, Crunch, and Roar. Or do something crazy like a Dustox or sumthing. Yeah, not greatest stats, but lots fun...Dustox with Silver Wind, Toxic, Moonlight, and Light Screen. I dunno, just have fun!