>>16629233A lot of this is personal preference, but:
-Change your HP EVs for each poke to ensure that each has an odd HP value. If you end up with four free EVs, give them to either defensive stat or a boosted but not-maxed stat.
-For Trevenant: drop either Horn Leech or Leech Seed for Curse.
-For Jellicent: choose a Naughty nature and invest in full SpD. Give the remaining four EVs to SpA.
-For Sableye: drop Will-O-Wisp for Swagger. I normally wouldn't recommend Swagger, but it has excellent synergy with Foul Play.
-For Tangrowth: Drop the Assault Vest and SpD investment. Give it and Adamant nature and full Atk investment. Give the remaining four EVs to Def.
-For Heatran: Honestly, I'd drop it for a classic spinning Donphan, but if you want to stick with it, get rid of Flash Cannon for either Protect or Substite and swap Fire Blast for either Lava Plume or Flamethrower (for consistency's sake). Also, those HP EVs could be better used elsewhere (e.g., swap with Spe or divide them among everything else), but it's up to you. I don't run Heatran, though, so take my advice here with a grain of salt.
That's about it.
