A turtle, that's what Izuku was, an energetic one at that. He can also turn into a human boy.

You were walking along the beach at night, and you see a flash of blue.

Thinking it's a villain, you run over to it. But you don't see a villain. You see a light teal turtle spinning in circles, emitting blue lightning and making smoke around it.

The smoke fully goes around him, and when it disappears, a human boy is in the turtles place, giggling and only wearing shorts.