He kept the remote a secret

It was probably for the best if he didn't tell Mallow about the remote, at the very least for the moment. After all, he wouldn't just have to explain what it could seemingly do, but also that he had already used it on her without her knowledge, even if it was on accident. Thus, Ash decided to lie about the device in his hand, keeping it to himself.

"Oh, it's nothing," he told the green-haired girl. "It's just an old toy I've been keeping on me for a while as a keepsake of sorts."

"Okay, but why would you take it out now of all times?" Mallow reasonably questioned.

"I never actually took it out of my bag the entire time I spent in Alola," Ash made up his excuse on the spot. "Now that I'm back in Kanto, I just got the thought that I should probably check on it after so long, you know?"

"Well, if you say so," she shrugged, deciding to stop her inquiry and not pay any further mind to the remote for now. "Anyway, we should probably get moving again. Didn't you say it wasn't too much further until the next Pokémon-Center?"

"Right, I did," he recalled his assessment from earlier in the day. "We should be able to get there by evening."

"Great, then let's get a move on!" Mallow exclaimed, turning around and slowly getting into a walk again. "I can't wait for dinner, even if it might not be your cooking tonight."

With Mallow's back turned towards him once more, Ash had to consider his options. It would be weird if he just stayed behind her for the entire walk to the Pokémon-Center, so if he wanted to do anything with the remote before they got there, this was most likely his only opportunity. Especially since he figured that he had to aim the remote at someone in order to use it on them. If he tried to do that right next to Mallow, she would surely notice and start asking questions.

What should he actually do with it though? Granted, he could simply use the same button as before to try to return everything to normal, but he would be lying if he denied his growing curiosity about just what else the device was capable of. Then again, the potential risk seemed fairly high, so it might as well be best to put further experimentation on hold and not use the remote for now.