Collax was about to return his team and enter the house when a Rhyperior, and a rather questionable one, suddenly burst out of literally nowhere and began assaulting the various trainers before him. In the split second that JC began counterattacking, Collax grasped back onto Barkley's head branches and drew a machete, raising it with a rallying cry.
Three more figures appeared from the fog of the forest, each from a different direction. One came rumbling forward with a roar- A Drapion. Another floated forward and shone a number of entrancing lights on its stomach- A Malamar. The third drifted closer from above- A Mismagius. All of them locked eyes on the Rhyperior, and each prepared their own separate attack. They had all been trained by Collax to react independently and work together. Collax, still, spouted commands to his team of Pokemon.
Barkley was already ahead of the game. After JC's various attacks pummeled it, the Trevenant's eye shone vivid purple as an array of purple vines erupted from the ground around the Rhyperior, snagging and entangling it with Forest's Curse. Then Collax turned his attention to the rest of his Pokemon team.
"Viola, Fiery Dance! , Duke move after Viola and blind it with Silver Wind! Lan, hypnosis! Scrat, break it down with Crunch, and Majia, use Mystical Fire to make sure it stays down!"
The team of Pokemon under Collax's command moved in unison. Viola the Volcarona flapped her wings violently, kicking up a storm of flames that jetted the Rhyperior, which (thanks to Forest's Curse) would take significant damage if they landed. Immediately afterwards, Duke the Ledian buzzed up above Viola, sending out a spray of white dust that targeted the Rhyperior, wherever it happened to be. He wasn't aiming to damage the Rhyperior, but given it's new grass-type thanks to Forest's Curse, the bug-type move Silver Wind may do more damage than usual if it too landed, though it was aimed at the wild Pokemon's eyes. As Duke released the Silver Wind, Lan the Malamar floated around to find the Rhyperior's face, immediately flashing his array of hypnotic lights in an attempt to send the drill Pokemon to sleep.
Whether or not any of this succeeded, the rest of the team followed up as well. Scrat, the titanic Drapion, rumbled forward and dove to chomp down on the Rhyperior with Crunch. Should he be successful, Scrat would quickly push the wild Pokemon away from him, in hopes that Majia, who had ignited flames around her, would have a clear shot at the Rhyperior with Mystical Fire, which would also be significantly more powerful thanks to Forest's Curse.
Collax hadn't always been great at Pokemon battles, and he still wasn't exactly the best, but his time on the deserted island region had changed him. His experience with the ingenious battler Madison had given him many more setups and preparations, battle plans, and more. It was partially thanks to her that he had developed the battle strategies he had, and thanks to his team of Pokemon, he was able to pull them through. Collax was prepared in case any of this assault failed, but he was mildly confident that his team knew what they were doing. This wasn't the first time they'd been in situations like this, after all.
[TL;DR] Barkley used Forest's Curse, Viola used Fiery Dance, Duke used Silver Wind to try and blind it, Lan used Hypnosis in an attempt to put it to sleep, Scrat used Crunch on it, and Majia used Mystical Fire. All in that order, in hopefully quick succession.