Gym leader rosters:
Gym 1
Cilan, Cress, Chili: Triple battle/Rotation battle. The three at once.
Pokemon: Pansage, Pansear, Panpour.
Rematch team (You fight them separately this time):
Cilan- Simisage, Cacturne, Sawsbuck, Ludicolo, Vileplume, Tropius
Cress- Simipour, Crawdaunt, Jellicent, Tentacruel, Slowbro, Lapras
Chili- Simisear, Houndoom, Darmanitan, Magmortar, Magcargo, Torkoal
Gym 2
Lenora: Harder puzzles, actual riddles involved.
Pokemon: Watchog, Herdier, Audino
Rematch team: Stoutland, Watchog, Blissey, Bibarel, Girafarig, Togekiss
Gym 3
Burgh: You have to beat each trainer in the gym who will then summon their bug type Pokemon to clear away the spider's webs that appear instead of the honey. The honey walls are still there a little as well.
Pokemon: Whirlipede, Dwebble, Swadloon, Leavanny
Rematch team: Volcarona, Leavanny, Scolipede, Crustle, Scizor, Heracross
Gym 4
Elesa: There are more trainers in the gym, and the circuit is more complicated.
Pokemon: Emolga, Zebstrika, Emolga, Tynamo, Joltik
Rematch team: Zebstrika, Emolga, Galvantula, Eelektross, Lanturn, Luxray
Gym 5
Clay: Clay's gym is now a complicated system of Excadrill tunnels.
Pokemon: Krokorok, Stunfisk, Palipitaod, Excadrill
Rematch team: Krookodile, Seismitoad, Excadrill, Garchomp, Mamoswine, Rhyperior
Can't be bothered to do the others.