Despite that you are surrounded on Team Plasma G’s ship, Hugh and Cheren turn to you, and Hugh warns you that he's going to 'unleash my rage!'  Hugh heads South and Cheren North, leaving you in the center- approached by one of the Team Plasma G members.

Battle: Team Plasma Grunt (1200 Poke)
Opponent: Koffing Lv 30

Be a bit wary- while the Koffing isn't too bad, it has both the poisonous Sludge attack and the ability to use Haze to clear out stat changes.

Defeated, the first Plasma G grunt calls for the next one- who calls it 'Trubbish time'.

Battle: Team Plasma Grunt (1200 Poke)
Opponent: Trubbish Lv 30

Stunned, Team Plasma are reminded of 'that trainer' who bested them two years ago, and the second grunt backs off.  You are now free to rearrange pokemon and move around again, so go talk to Hugh.  Your friend is confident he can handle his end of things, and tells you to go help out Cheren.

Cheren wants to show what you and he can do, so he asks you to join him in a 2v2 battle.

Battle: Team Plasma Grunt and Team Plasma Grunt (2320 Poke)
Opponent A: Golbat Lv 29, Liepard Lv 29
Opponent B: Grimer Lv 29, Krokorok Lv 29
Cheren: Stoutland Lv 33

Cheren's Stoutland comes with both Strength and Thunder Fang, and between those and the herd dog's staggering toughness, the battle is pretty trivial.  Liepard in particular goes down fast, but that's mostly on account of its suffering from Floatzel Syndrome (i.e. it's offensively strong and looks cool, but easier to break than wet tissue paper).

Cheren thanks you for your help, telling you you've gotten very strong, and then sends you to help out Hugh.