Ema
Cas grins at Yari's reaction. Seeing her go from lethargic to extremely animated fills him with joy. Bringing joy and excitement to others is something Cas always attempts to do. Yari's reaction gives him pause for a minute, though. It occurs to him that Yari is essentially waiting to try beat him up, but he pushes that thought away.

He immediately runs over to the far side of the arena, waiting for Yari to stand at the opposite side.
"Yo, so let's do this! Never sparred with someone beofre, so it should be a learnin' experience"
Barbara
She giggles childishly in glee with her unfittingly deep voice, said giggle also had very faint hints of malice in it as she skipped to the other end of the arena and stopped there. "I'm ready! She waved excitedly at Caspar and would stand still, waiting for something to happen. "Wait, when do we decide its over? While I would love to beat the shit out of people right now, I also don't want to leave you with permanent damage just for wanting to have a practice fight!" 

[How big would you say the arena is? A square would be best, maybe a large space, say 52x52ft, or 16x16m or is this too large for your taste?]
Ema
[Think that size works 👍 ]
"Permanent damage?" Asks Cas. "C'mon, gimme some credit! I've been beaten up before, I can take it again." True, Cas *Had* Been beaten up before, but it had been when he was like, ten. Still, he does privately steel himself for some sort of big attack from Yari... Just to be safe

Ignoring Yari's unfittingly deep voice, Cas gives her question some thought. "Uhh... Guess we just keep going till one of us looks like they're about to pass out? Or I guess we could just say when we're too fucked up." Cas looks over at the edge of the arena, which gives him an idea. "What if we try force eachother out the ring? Ends on a ring-out, like sumo. Or gameshows or something."
Barbara
"So what I hear is, it's over when one of us is too beat up to continue, when one of us is forced out of the ring, or when one of us gives up." She lists them out, then her arms and hands flap limply in excitement. "Let's go! Do something!" She hops in place as she waits for Caspar o Do A Thing.
Ema
"Ok... Here goes nothin'...!"
Cas plants his legs firmly on the ground and focuses on Yari. He quickly raises his arms, firing a tight stream of blue particles at Yari. He's not entirely sure what he intends to do with this frosty blast, other than just... Generally inconveniencing her. Suppose it'll help him learn what she can even do, anyway.

G1 uhh ice blast thingie?
Barbara
Yarimiel remained quiet and would say few words from here on. She would use her ability to lay flat on the ground and skitter to the side, looking like a very burnt pancake until she popped back up from the move, the momentum from suddenly reforming launching her into the air about a foot before landing again and falling on her side. "Wow! That was cool!"
Ema
Cas stares for a moment, before unleashing his finger guns. "You can say that again! Alright!" He says, a wide, stupid grin on his face. Cas was, essentially, just called 'cool' by someone else, and it's already going to his head just a little. He may not look cool right now, having whiffed his attack and all but goddamnit he *Feels* Cool, and that's what matters in the end, right?.
Anyway, Cas's little pose has left him a open. Perfect opportunity, right there.
Barbara
Yarimiel would attempt to cover the full sixteen or so meters as fast as possible by extending her arms forwards and latching (via suction) onto the nearest spot on the ground to the middle, then she'd use this to pull herself forwards violently, pulling an arm back towards herself and using the momentum of *That* To extend it once again towards Caspar in an attempt to grab him anywhere on his upper body, her fingers having extended dramatically as well as her hand, now looking like a giant webbed limb.
Ema
"Heh, p-r-e-t-t-y co- **JESUS CHRIST**" Yells Cas, not expecting the giant webbed hand encroaching on his general area. He quickly flings himself back, sliding across the ground on a thin layer of ice. He quickly gets to his feet, steeling his nerves once again. "Woah! Nearly got me there... Should'a been concentrating..." Cas notes that Yari doesn't need to move from her spot to get him... Which doesn't bode well for his success. A hard counter to his mobility, too... This would require some strategy.
Barbara
She giggles again from his reaction, and landed on her feet, skidding to a stop before standing upright again.

Yarimiel would yet again send out her arms using her power, but now that she was closer, she was able to attack. She used them to overshoot Caspar and unite hands behind him in an attempt to pull him closer. If she managed to make contact, they would bind to him and pull closer. Otherwise, they would immediately retract with even greater speed. "Get over here!" Was spat out in a low, grumbly voice. A simple imitation of a famous line.