DISCLAIMER: Korra ain't mine.
I think there was some episode where Aang and Katara had a snowball fight, but I don't remember. ^^;
"Sifu Katara!"
The old woman turned, a greeting on her lips as the younger bender dashed up to her and, panting, dropped into a bow. "I'm so sorry I'm late; Naga ran off in the middle of the night chasing penguins and I couldn't rest until I found her and then one of my mittens fell off in the water and I had to get another pair and—"
Katara laughed and waved Korra off, stooping slightly to set a hand on the dark-haired girl's head (it had been years since her knees allowed her to get on and off the ground easily). "Don't trouble yourself, Korra, your mother told me you'd be a bit behind this morning. I thought we should take a break today. Not that I don't think you're up to training," she added quickly, seeing her pupil begin to frown, "but you've been working so hard, you deserve a rest. Besides, I did promise you we would have some fun together, didn't I?"
Korra nodded eagerly, springing to her feet. "Sifu, there's something I really, really want to do!" she exclaimed, bouncing on the balls of her feet. "But I—I don't know if you can do it with waterbending…" She bit her lip, excitement all of a sudden replaced with anxiety. Katara smiled and set her hands on Korra's small shoulders.
"Well, why don't we find out? What is it?"
Korra's blue eyes sparkled as she eagerly asked "Can we have a snowball fight?"
Oh ho. Katara chuckled. "Korra, even my husband wouldn't have had the courage to ask me what you just did. He found out the hard way that you never, ever challenge a master Waterbender to snowball fight!" As she spoke, the old woman lifted her arms, curling her hands so that her fingertips met. All the snow within a three-foot radius of the two benders lifted off the ground and condensed itself into several small spheres that immediately began hurling themselves at the young Avatar. Korra shrieked and covered her arms with her head.
"No fair, we didn't say 'go'!" she cried, yelping as some snow found its way into the collar of her parka.
"All's fair in love and war," Katara laughed, taking a few seconds to condense two snowballs into one. Korra dropped her arms and tried to send a wave of snow at Katara, but the elder bender easily turned it to pure water that simply dropped on the ground.
Approximately half an hour and one very cold Avatar later, Korra was sitting in Katara's hut with a cup of hot tea and a blanket around her shoulders. She'd bended the moisture out of her clothing, of course, but the garments were still freezing. Korra sighed and propped her head on her fists, watching Katara morosely as her sifu prepared some seaweed noodles. "How'd you get so good at that?" she grumbled, obviously stung from the loss.
Katara smiled, turning around and winking at her young pupil. "Lots of practice, Korra, and like I said, I'm a master Waterbender. I have my secrets."
"I want a rematch when I master waterbending!" Korra declared immediately, fixing Katara with a challenging look. Katara shrugged and smirked.
"All right, Korra, but don't be surprised if you lose again."
"Hey, how did your practice session with Master Kat—" Mako trailed off as a sopping wet and VERY grumpy-looking Korra tramped into the house. His eyebrows rose. "Um, what…?"
"Shut up, Mako," she growled, bending the water from her clothes and hurling it at him. He yelped as the freezing liquid splattered his skin.
"What did I do?" he demanded.
"She's just a sore loser." Katara was looking very pleased with herself as she shut the door to the house. Mako decided not to ask.
AN: The last bit is post-S1, just in case there was any confusion.