"Karith, it seems you are the only elder student who wishes to participate this term. I will be your partner, let's start with what the younger students are doing. Only, we will be on a slightly more dangerous and skillful scale. Assume your position."
Alex would let off a small laugh. "Just because you're in Slytherin doesn't mean you intimidate me." Alex would then take a step forward with her left foot and feint her wand to the right. Using this as a distraction, she would flick her wand back to the left, "Expelliarmus!Everte Statum!"
Karith would laugh, block the disarming charm with a silent shield charm, then dodge to the left to avoid the flying spell. He would the point his wand at Alex, and send a silent stunning spell towards her, while moving to his left. Without stopping to see if it hit or not, he would conjure a snake from his wand with "Serpensortia", which would fall behind her leaving her in between him with his wand still ready, and the snake.
Alex would immediately go into a protective stance. "Haha, the problem with you Slytherins, you always use the dangerous spells. And you forget, Lemurs are fantastic at dealing with snakes!" Alex would cast 'Anteoculatia' at Karith as she dived to the side. In midair, she'd sheath her wand and turn into a Lemur. She'd then attack the snake and strangle it. Staying in Lemur form, she'd circle around Karith.
Karith would grin. "Well, you can't use spells in that form, so for me to just stun you would be a bit unfair. However, don't you know lemurs are rodents...?" With a wide grin, Karith would stow his wand, and transform into his Oscelot form, and begin stalking the small rodent, and attempt to pounce on her, though she would notice his claws were sheathed.
Alex would revert to human form, but only to say, "Actually, genius, they're primates." She would then go back into Lemur form and she would take a very defensive form. She would think to herself, I need trees, trees with very tight-knit branches. The Room of Requirement would realize her need and trees would form around her. She would leap into the trees and seem to disappear.
Karith would laugh to himself, which would come out like a contented purr...he may not know a lot about her "primate" form, but she apparently didn't know much about his either. Oscelots were made for the trees...they spent most of their lives in the trees, and could even climb down a tree head first. He would just have to remember to pull in his climbing claws before he pounced. He would jump up into the trees, searching for Alex with his eyes, scanning for the slightest movement. He would see her darting between the tree branches, and jump, attempting to land on the same branch he was on. This dual was turning out to be more fun than he had
thought it would...he so rarely turned into this form.
"Meep!" Alex would say, then she would just down from the branch and roll away. She was lucky she learned how to travel by rolling when she did. She immediately bolted off and hid. She awaited the next move made by the ocelot.
Karith would slink through the branches, his cat eyes roving the knot of trees. He would move slow and sinuously, a predator on the hunt, eyes always looking for movement in the branches. He would slowly move from branch to branch, looking for the creature attempting to hide from him.