Sometimes people say the first time we see Goku turn SSJ2 in the series was when he fights against Vegeta in the Buu Saga.
However, there is a chapter before that when you wonder if he was SSJ2 or not. In his battle in Other World against Pikkon, when he first turns into SSJ2 we see the electricity sparks we see in SSJ2 transformations and his hair is seen more rigid than usual.
But after the initial transformation and power up, we no longer see electricity sparks on him. Was Goku SSJ2 when he fought against Pikkon or was he a regular super saiyan?