Oh, good.

...Is he allowed to go back and get her healed at the Pokémon Center?

Unclear!

"Is the expectation that I complete the entire gym in a single attempt, or can I leave after every battle?"

"It's not technically against the rules but it's kind of discouraged. And you won't be able to leave midway through an Elite 4 challenge, so if that's something you're aiming for it'll be better practice this way."

Unfortunate.

He heads over to the leaf circle.

The second curtain rises.

Behind it there's a curtain with a leaf on it, three more identical circles, and a waitress carrying two Pokéballs.

By process of elimination, presumably he's supposed to step on the red circle. Unless it's a trick question or something. Is the waitress going to stop him?

She's going to try!

"You may have beaten Maxwell, but are you ready for your second course?"

She sends out a Patrat.

He sends out Amadelphous. Same strategy as usual.

Her Patrat doesn't have much practice in real battles. It manages to get in one solid attack before going down.

She sends out a Purrloin next.

Oh, it's a purple cat thing. Well, purple cat things are just as vulnerable as everything else (except sentient rocks?) to being hit.

The purple cat thing has some tricks! It can imitate techniques that the waitress's other Pokémon know! But yes, hitting it will work perfectly well.

By the time he's finished defeating the cat thing, Amadelphous has clearly taken a few hits, but she's not majorly injured. She's probably at about half her full strength.

Hopefully he's almost done.

He steps on the red circle.

It was not a trick question! The curtain lifts, revealing a stage. 

On top of the stage are three men, who all look a couple years older than Sebastian. They look mostly similar, but one has green hair, one red, and one blue.

Oh no, does he have to fight three people? He's not sure Amadelphous can take that. Maybe he should have gone back to the Pokémon Center, whether or not it's "encouraged."

"So, as you may have noticed, this isn't an entirely normal gym," says the green-haired one. "Instead of specializing in a single type, each of us has a different focus. I'm Cilan, and I focus on grass-types."

"I'm Chili," says the red-haired one, "and I'm a fire specialist."

"And I'm Cress," says the blue-haired one, "and I mainly specialize in water-types. ...Though of course, we don't just use those types."

"In order to decide which of us to battle, we'll need to know what your starter Pokémon was, and how many gym badges you have already."

He ... has no idea what his theoretical starter Pokémon that got stolen would have been.

"My starter was an Audino, and this is my first time challenging a gym."

Cilan looks surprised, though it's not clear which part of that was surprising. He glances at the other two.

"I'll take him," says Chili. "Hardly anyone's been picking Grass-types these days."

The other two move out of the way. Chili selects two Pokéballs, and sends out a Lillipup.

Have the dogs been fire-types this whole time??? He had sort of assumed that types had ... anything to do with the actual characteristics of a Pokémon.

He sends out Amadelphous.

(No, they're Normal-types, but there's only so many fire-type Pokémon that are appropriate for a zero-badge battle. Most people with zero badges are ten-year-olds who've just started their journey.)

"Amadelphous, use Double Slap!" 

She charges the Lillipup, hitting it three times.

"Lillipup, use Bite!"

The Lillipup nips at Amadelphous. 

"Amadelphous, use Double Slap again!" Probably he will eventually encounter a reason to do literally anything else but today does not seem to be that day.

She hits twice this time.

The Lillipup looks pretty winded, but it's still on its feet.