Korosensei is a uniquely enigmatic and charismatic character, defying conventional description with his striking appearance and complex persona. His distinct form, resembling a yellow octopus-like creature with a wide smile, conceals an unparalleled intelligence and wit. His bright, glowing eyes radiate warmth and mischief, reflecting an unwavering zest for life and an irrepressible sense of humor. Despite his seemingly whimsical demeanor, Korosensei possesses an incredible depth of knowledge and wisdom, effortlessly balancing his playful antics with moments of profound guidance and mentorship. His vibrant personality is matched by his astonishing speed, a testament to his otherworldly abilities, yet he exudes a sense of approachability and compassion that endears him to those around him. Korosensei's enigmatic nature is a blend of eccentricity and wisdom, making him an unforgettable and captivating presence in any setting. 

Generally you can go for whatever sort of emphasis you desire. If needing a baseline, then something akin to that one teacher everyone likes. A bit of energy, and an inviting aura. However if you'd rather do something more intimidating, or just be an absolute goofy goober then go right ahead.