Okay, Grass is hard because of the number of weaknesses they have, but here is my suggestions.
I'm not including items or EVs as they are usually not important in game.
Virizion
- Sacred Sword/Close Combat
- Swords Dance
- Leaf Blade
- Aerial Ace (deals with Marshal, but it can get X Scissor or Stone Edge if you prefer)
Ferrothorn
- Leech Seed (its an Egg Move) or maybe Hone Claws or Curse if you don't want to breed
- Power Whip (its accuracy is improved if you give it Hone Claws)
- Thunder Wave
- Shadow Claw (don't ask me how it can use it!) - deals with Shauntal and Caitlyn
Shiftry
- Extrasensory
- X-Scissor
-Dark Pulse (move tutor) or Foul Play
- Leaf Storm/Aerial Ace/Rock Slide
Abomasnow - this is largely to deal with Iris
- Blizzard
- Wood Hammer
- Ice Shard
- Shadow Ball/Earthquake
Rotom-Mow
- Thunderbolt
- Shadow Ball
- Will-o-Wisp
- Signal Beam (move tutor)
Ludicolo
- Surf/Hydro Pump
- Ice Beam/Blizzard (if you give it Blizzard, only use it after Abomasnow, as it will have 100% accuracy, thanks to Snow Warning)
- Nature Power (it becomes Earthquake during the E4)
- Focus Blast/Brick Break (Its Special Attack is higher, but you might prefer the reliability of Brick Break anyway)
If you are worried about residual damage from Hail, then give Ludicolo Ran Dance, or Shiftry Sunny Day, as both can make use of those weather effects, and they don't damage the other Pokemon on the field. I didn't want to get rid of an attack to do that, though.
Hope this helps.
