I tend to feel Sonic stories ought to have a 'version of reality' explanation attached to them, there's so many variations of canon. This one though could fit almost anywhere among the various canons that include Shadow as a bad guy (at least initially)
"This is stupid." Knuckles stood with difficulty, clinging to a sapling and staring at his feet. He was having an alarming amount of difficulty keeping them from sliding off in opposite directions. Again. He had suffered exactly that once already, resulting in a painful fall onto his tail which he now had firmly tucked between his legs. "Just what this undignified little exercise is supposed to achieve?"
"Know your enemy?" Sonic suggested. He didn't look much better off, unsuccessfully attempting to achieve some forward motion on the newly acquired hoverskates. "The things seem to work well enough for Shadow."
"Yes, well," Knuckles let go of the sapling and pushed off gently, concentrating on remembering how the black hedgehog had moved. "He probably didn't have to learn it did he? For all we know it was--" He waved a hand vaguely which quickly upset his balance and turned into a frantic flail until he recovered and continued, "--hard wired in or something."
Either Sonic's naturally good coordination or usual complete lack of caution had come to the fore and he struck out across the meadow at a passable speed, swung round and headed back towards the small wood where Knuckles was still progressing from tree to tree for support.
Sonic whooped as he approached. "I could get used to this."
Knuckles floundered of out of the way, coming to a halt after rotating gently on the spot several times for no reason that he could control. He surveyed Sonic's high speed approach with raised eyebrows.
"Impressive," he allowed. "Now just how are you planning to stop?"
Sonic's face fell. "Ah."
Knuckles managed to turn around in time to see Sonic grab the first tree he passed, orbit it at high speed, tearing one glove off in the process and come to a skidding stop on his knees.
Knuckles skated slowly over and drifted to an awkward, but upright stop beside him.
"You're about to tell me you meant to do that aren't you?"
Sonic picked himself up, still grinning. "Where's your sense of adventure, Knux? Don't you ever try something new just for fun?"
"This is fun?" Knuckles asked, rubbing at the base of his tail and looking pointedly at Sonic's skinned knees.
Sonic dismissed that with a grimace. "What's a few scrapes and bruises? That's what adrenaline is for." He shrugged. "Anyway I've had worse, and I know you have too, so what's the big deal?"
"I can not afford to get injured larking about, Sonic! Unlike some, I do have some sense of responsibility!"
Sonic pulled a face, "And here I was just getting excited because we'd gone a whole half hour without mentioning your precious duty. It's not like I sat on your head and forced you into those things, y'know."
"No you just talked my ears off until I gave in," Knuckles retorted.
"Oh is that what happened to them?" Sonic twitched his own ears in amusement.
"Oh lighten up. Anyway, we're not 'larking' we're 'researching' remember?"
"And has your 'research' turned up anything of use?" Knuckles asked drily.
"Absolutely. Sonic nodded, hauling himself back upright clinging to a branch. "In fact I have spotted two weakness." He grabbed Knuckles' arm and dragged him, protesting, to the treeline. "One: leverage."
"Two: acceleration." Sonic pushed off from the tree again and skated to the middle of the field, his rather ungainly start a more than ample demonstration.
Knuckles followed him, a bit surer of his balance now. "Shadow doesn't seem to have any trouble with acceleration," he pointed out. "I would hazard a guess that he is simply better at this."
Sonic made a derisive sound. "At the moment."
"'At the moment' is when we're likely to have to deal with him, Sonic. Unless you're planning on taking a holiday."
Sonic pretended to give that idea some thought. "Ice Cap might be nice. Should be a piece of cake skating the ice there are these things."
Sonic grinned broadly. Knuckles did not join him, instead opening his mouth to deliver some acerbic comment. He stopped at the sight of Tails flying full tilt across the field towards them, anxiety written all over his face.
"What's up?" Sonic asked the second Tails was within earshot.
"Shadow," Tails gasped out. "Trouble."
Sonic kicked the skates off instantly. "On the other hand," he said, his grin turning fierce. "Maybe we should stick to what we're good at."
This time Knuckles did allow a flicker of a smile to cross his face. "Where?" he asked Tails.
The fox pointed.
In moments the field was empty, the hoverskates abandoned in the grass.