Lake of the Sunne/Moone
An optional side area with not much to it, besides its sheer atmosphere. From the entrance, head north, then across the stone bridge to the entrance of the ruins. Inside, approach the north-east corner to find TM03 Psyshock, a neat special move that deals physical damage.
From here, you can continue north to reach the endpoint of this area, but right now, there's nothing to see. Either way, once you're breathed in enough of the atmosphere, exit back to Ula'ula Meadow. Then run back to the entrance and challenge the Golfer.
A user of the Flame Orb, a held item that inflicts Burn on its holder. Normally a bad thing, but it can be manipulated like you're about to see.
Hariyama automatically inflicts itself with a Burn once the first turn ends. Burn usually lowers a Pokemon's Attack, but Hariyama has the Guts Ability that negates this effect and instead boosts its Attack. Finish it quick with Flying, Psychic or Fairy-types.
Alakazam plays a little switcheroo by using Trick to swap its held item with your Pokemon's, thus giving your Pokemon the Flame Orb. Doh! It will also spam Recover while your Pokemon gets damage by its Burn. A good solution is to send a Fire-type as they cannot be burned.
If you're confident, you can also try and one-shot Alakazam before the Flame Orb kicks in. A Pokemon that knows Knock Off is great since Knock Off does more damage if a Pokemon has a held item and Alakazam will gain your Pokemon's held item.
Surpass the fiery ordeal and you'll receive a Flame Orb for yourself. Try not to burn yourself, alright?
Not counting the new Oricorio form, the only new Pokemon here is Ribombee, the evolved form of Cutiefly. This Bug and Fairy-type is speedy and has respectable Special Attack, but has the durability of a wet paper bag.