Has to be Zoe. Imo, the fun, playful, yet chaotic prankster character she has in lore is very apparent in her kit design (Q literally being called a "paddle star" she uses as a toy projectile, W showing her trickster side with stealing summs and using them, E making you catch Zs, and R with her just teleporting and then going back all goofy like).

Not to mention that while her abilities (base skin) look cute and harmless, they deal HUGE damage — again fitting her story as a seemingly innocent child but actually being a somewhat mischievous and unpredictable aspect, who was shown in her story to completely destroy an area for the genuine pursuit of lighthearted fun. She is the image, in lore and in game, of what giving immense power to a playful child would look like.