Severus really didn't see what the issue with the creature was. It was ugly, sure, and its tentacles were certainly a hazard, but it wasn't a dementor or anything too terrible. Severus watched Locke's acrobatics and melee attacks with an almost bored, unimpressed expression on his face. On one hand it was amusing; on the other, it was just plain silly.
Locke was thrown to the stage and Severus smirked to himself. He was about to cast a fire spell - since he'd been told that was the creature's weakness - but he was suddenly on his back, thrown to the ground by a sneaky tentacle the malboro had managed to wrap around his ankle. He let out a yelp, but held onto his wand.
"Sectumsempra," he growled and watched in triumph as the tentacle was sliced off and fell to the ground. It took him him a moment to work his ankle free and the monster gained on him drooling on him as it hovered over him. He felt ill the moment he felt the wetness on his hand. "Ugh," he grumbled as he wiped his hand on his trousers. The malboro obviously had some sort of venom. "Incendio," he cast. The malboro roared in anger, and Severus used the distraction to get to his feet and give the creature some space as the fire consumed it.