The Volcarona looks interesting, and this looks like fun! Might as well give it a shot;
Sawsbuck
Magic Guard
Jolly/Impish
@Leftovers
252HP/4Atk/252Spe
-Leech Seed
-Substitute
-Megahorn
-GrassWhistle/Horn Leech/Wild Charge
This is your typical SubSeed set, and Sawsbuck should be able to pull it off quite nicely. The idea is the same as always; cripple the opponent with GrassWhistle, set up a substitute, fire off Leech Seed and repeat when necessary. Sawsbuck can pull this off quite well thanks to his base 80 HP and 95 Speed, allowing him to quickly set up on most opponents before they can even react. Megahorn is used to deal with those pesky grass types who are immune to Leech Seed and works off his decent Attack stat. Magic Guard is an extremely useful ability that compliments this set well, preventing Sawsbuck from taking any extra damage from the weather and status effects like poison.
If GrassWhistle's shaky accuracy bothers you too much, then you can always run a second attack move in the last slot. Horn Leech is a nice option with Stab and recovery, but using it means that Sawsbuck is walled by Steel, Fire, and Flying types. Wild Charge is another option, being able to hit all those types(assuming they're not part Ground) and having no recoil damage thanks to Magic Guard.
The EV setup is pretty basic; max HP to make the substitutes as bulky as possible, max speed to try and outrun the opponent. The rest are put into Attack to add a little kick to Sawsbuck's offense. If you prefer, a more defensive setup is viable off of Sawsbuck's base 70 Defenses with 252HP/132Def/124SpD and an impish nature.
Sawsbuck appreciates entry hazzard support, as he is likely to cause a lot of switches. Toxic Spikes may be the best option to rack up a lot of indirect damage, however, Stealth Rock could also cause a lot of damage since many of the types Sawsbuck is weak to are weak to Rock. Crustle provides good entry hazard support with Spikes or Stealth Rock, while Tentacruel can cover Toxic Spikes detail. It also wouldn't hurt to have a bulky Water type to handle any Fire types that Sawsbuck is bound to drag in, and a good Flying type to cover the Fighting/Bug types. Some help with bulky grass types would also be quite useful to eliminate any threats to Sawsbuck's Leech Seed.