And he appears directly in front of of a not very thoroughly clad girl who has her arms extended to both sides, holding a staff in her right hand. The girl and several other people are on a circular platform on a hill, surrounding a giant unfriendly-looking plant.

The girl's eyes widen in surprise, but she doesn't move as a show of lights around her continues.

The lights reach into the sky, parting the clouds and opening a neat circle there, from which a large... winged... thing... starts descending.

The mysteriously appearing person looks at the large winged thing and blinks!

He is wearing a black t-shirt and jeans. He also has white, feathery wings, folded against his back.

"Valefor, Fire," the girl calls softly.

The air around the flying (floating, really, it's not using its wings to stay aloft) thing shimmers and it gestures towards the unfriendly-looking plant thing. Following that movement, a flame appears on the plant.

And the air around one of the other people around shimmers similarly, and another flame appears on the plant.

"Who are you, and can you help?" the girl asks the angel as one of the plant's tentacles lashes out like a whip at the flying thing—Valefor—who dodges it by flying higher.

"Help– what, kill the weird plant?"

"Yes."

The air shimmers around someone else—lots of light effects here, huh?—and his sword starts glowing. He runs towards the plant thing, dodges one tentacle and severs another—but is swatted aside and hits the ground with a crash.

He drops his apple – he hardly needs it, what the heck – and flies plant-wards, turning the nearest tentacle into cloud-fluff.

*failing to turn the nearest tentacle into cloud-fluff, he means.

The girl does a magic thing, and the guy who was hit by the tentacle is covered with sparkles.

He jumps to his feet immediately and runs around the plant.

… Theo is slightly surprised by the fact that the nearest tentacle is not changing, and tries to change another part of the tentacle.

He fails! Also the tentacle the blond boy severed starts dissolving into balls of light that fade as they float up. And the two spots of flame on the plant thing disappear of their own accord, leaving a mark much less scorched than it ought to be, plus some more balls of fading light.

… And if he tries to change the scorched bit into cloud fluff, can he change any of it or is this thing somehow totally invulnerable to this – what the hell.

Nope, this thing is somehow totally invulnerable to this.

"What are you doing?"

More short-lived fire!

… He will not in fact try acid on it in case it does something weird to that and stops him from changing it back. Instead he will try– ugh, what the hell doesn't hurt wildlife but would kill this freaking plant.

Next time there's fire on the plant he makes it hotter and larger and stretch further on the creature, unless it nullifies him in an area around it.

Well, it takes a while longer than he'd expect it to—almost as if there was in fact less fire there to work from than he can see—but it does work.

And then after a few seconds a large chunk of the fire's gone, leaving only the bits he's expanded.

"Was that you?"

He doesn't want to kill it, he won't burn it to death, he can try to char the tentacles and then cauterize the wounds if that applies or alternatively shove something solid against them to prevent it bleeding out or whatever, since it apparently doesn't totally nullify his abilities.

"Yes," he responds. "What the hell."

It... doesn't really have blood. Just the fading light things that leave its wounds, and they continue leaving its wounds when he tries to "cauterize" them.

One of the people around, holding a blue ball with bumps, spins it on his finger, causing black smoke to surround it. He throws it up in the air, jumps, and kicks the ball towards the plant thing, hitting it with significantly more force than kicking a ball should be able to apply. The cloud of black smoke grows and starts surrounding the plant, and from its tentacles' movements this seems to have impaired its vision.

He isn't sure how the flames will interact with the smoke – hopefully not explosively but he's not sure he should trust them to know with whatever the heck they're using against this thing, so he stops fanning the flames and instead flies back a bit – he has range, he can do stuff to it from a distance away, even if it's not a ridiculous distance.

There are in fact no explosions! Just the black cloud while the others continue doing fire or physical attacks while the plant lashes out at people.

At one point it starts moving in a very suspicious way and then a green very noxious-looking gas starts escaping from its body to surround the attackers.

Is this noxious-looking gas also invulnerable to his powers? Because if not he will clear it totally fine.